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Review 2017-2018 - Volume 56

The US Strike of 7 April 2017 and How it Influenced the Law on the Use of Force
PhD, Institute of Law Studies, Polish Academy of Sciences

Table of Contents
  1. The Reasons for the Strike of 7 April 2017 under Public International Law – Was it Lawful?
    1. Humanitarian Grounds
    2. The Vital Security Interests of the United States and its Allies 8
    3. The Chemical Weapons Convention and UNSC Resolutions
  2. States Reaction to the US Strike
  3. The Law on the Use of Force after 1945



On 4 April 2017, the chemical agent sarin was used against the civilian population in the town of Khan Sheikhun in Syria. According to the report of the Independent International Commission of Inquiry on the Syrian Arab Republic, at least 83 people were killed, including 28 children and 23 women, and another 293 people were injured. 1 In response to that attack, on 7 April 2017 the US conducted a strike on the Syrian military base Shayrat near the city of Homs since, as the US officials claimed, the aircraft that carried out the chemical attack took off from that military base. 2 The US fired 59 Tomahawk cruise missiles from two US warships, the USS Ross and USS Porter, stationed in the eastern Mediterranean Sea. Different sources reported about thirteen causalities following the attack; four from among military personnel, as well as nine civilians killed. Information about the material damage was equally vague – some sources mentioned that the base was seriously damaged, while others claimed that the base was left practically intact. 3

The attack constitutes an example of the unilateral use of force between States. However, it noteworthy not only for this reason, but also bearing in mind the scant justification given by the US administration for the strike, as well as the reaction of the international community. When it comes to the current regulation of the use of force, as established under the UN Charter, the only exceptions to the prohibition of the use of force are the right to self-defence, under the restrictive criteria of Article 51 of the UN Charter, as well as collective action, authorized by the United Nations Security Council (UNSC). State

* The Author is very grateful to the Reviewers for their insightful comments which helped to finalize this article. Back
1 Report of the Independent International Commission of Inquiry on the Syrian Arab Republic, A/HRC/36/55, § 75. Back
2 In its report released in August 2017, the Independent International Commission of Inquiry on the Syrian Arab Republic stated that there are “reasonable grounds” to believe that these were the Syrian forces which launched the attack (Report, supra note 1, § 77). However, contrary to early statements of the US, this conclusion was drawn after the examination of many pieces of evidence and was not based only on allegations. It is also interesting to note that the Commission, despite examining the cases of the use of force in Syria from the perspective of their compliance with international law, did not assess the legality of the US strike; the Report only mentions the fact that such strike took place (Report, supra note 1, p. 4, footnote 2). Back
3 USA Today, ‘U.S. missile strike on Syria: Here’s what we know’, 7 April 2017,; N. Khomami & J. Grierson, ‘US military strikes on Syria: what we know so far’, 7 April 2017,; Al-Marashi, ‘Trump's strike on Syria: A convenient distraction’, 8 April 2017, Back


practice has proven that the UN Charter norms on the use of force are also currently reflected in customary international law (CIL). 4 In addition, a unilateral intervention could also be legal if the State, where the intervention took place, consented to it or if there was a treaty norm allowing for the use of force. 5 However, none of these legal grounds can be used to justify the US strike.

The thesis advanced in this paper is that the conduct of the US on 7 April 2017 breached the prohibition of the use of force. Moreover, despite the fact that since 1945 there have been numerous cases of such breaches of the prohibition, the US strike seems to be an especially flagrant case of the infringement of Article 2(4) of the UN Charter, both because the US did not seek to prove its legality under international law, as well as because the strike constitutes an example of a unilateral police action. Despite these serious concerns, the action has been accepted by the group of States, which can potentially launch a new paradigm of the law on the use of force.

To explore this thesis, the article is divided into three parts. The first part discusses the justification of the intervention, as invoked by the President of the United States, Donald Trump, and supported by other US officials. The second part presents the reaction to the attack by the rest of the international community. Finally, the last part highlights the most important characteristics of the approach adopted by States when it comes to the prohibition of the use of force post-1945, as well as compares the conclusions drawn from this approach with the circumstances of the US strike of 7 April 2017.

I. The Reasons for the Strike of 7 April 2017 under Public International Law – Was it Lawful?

Soon after the attack, President Trump issued a statement on the reasons for the strike. 6 Even though he did not explicitly indicate any legal grounds for the attack, one may argue that at least three reasons underlying the operation may be constructed from his statement. 7

4 Such view is presented, inter alia, by A. Randelzhofer, ‘Commentary to Article 2(4)’, in B. Simma (ed.), The Charter of the United Nations: A Commentary (Oxford, OUP, 2002), p. 134; T. Hillier, Sourcebook on Public International Law (London, Cavendish 1998) p. 595; C. Kreß, ‘Major Post-Westphalian Shifts and Some Important Neo-Westphalian Hesitations’, Vol. 1 No. 1 Journal on the Use of Force and International Law 2015, p. 40; E. Gordon, ‘Article 2(4) in Historical Context’, Vol. 10 Yale Journal of International Law 1984-1985, p. 275; M. Shaw, International Law (Cambridge, CUP, 6th ed, 2008), p. 1123; I. Brownlie, ‘“International Law and the Use of Force by States” Revisited’, No 1. Chinese Journal of International Law 2002, p. 1; S. T. Helmersen, ‘The Prohibition of the Use of Force as Jus Cogens Explaining Apparent Derogations’, Vol. 61 Netherlands International Law Review 2014, p. 175; A. Cassese, International Law (Oxford, OUP, 2nd ed, 2005), p. 56. Back
5 Institute of International Law, Military assistance on request – resolution, 8 September 2011 r., Article 4. State’s consent for the use of force on its territory “flows from major principles of general international law: the principle of consent and the legal personality of the State producing the request for, or consent to, intervention” (I. Brownlie, ‘The United Nations Charter and the Use of Force, 1945-1985’, in A. Cassese (ed.), The Current Legal Regulation of the Use of Force (Dordrecht, Martinus Nijhoff, 1986), p. 501). Unless the State’s consent is explicit, specific and expressed freely, a State may consent to the use of force on its territory ad hoc or in a treaty provision (however, if the consent is granted in a treaty, a State should confirm it ad hoc either). Consent is not an exception to the prohibition n of the use of force, but an independent tool without which international law cannot function. Thus, when there is State’s consent, the use of force violates neither the sovereignty of the State where the force is used, nor the prohibition of the use of force ab initio (International Law Association, ‘Draft Report on Aggression and the Use of Force’, p. 14, Thus, there is no contravention between the consent for the use of armed force given by a sovereign State, under conditions as mentioned above, and the prohibition of the use of force from Article 2(4) of the UN Charter. Back
6 ‘Statement by President Trump on Syria’, 6 April 2017, Back
7 This article distinguishes between legal and extra-legal considerations, including morality, politics etc. What are the criteria allowing this differentiation? Certainly, it is indispensable to analyze the text of the declarations made by States – if a State refers to “formal sources of law, or to a legal concept or institution” (T. Ruys, ‘Armed Attack’ and Article 51 of the UN Charter: Evolutions in Customary Law and in Practice (Cambridge, CUP, 2010), p. 36), one may assume that it invokes legal argumentation. Moreover, a State may refer to legal reasoning not only when it explicitly claims that it used force in self-defense etc., but also when it states e.g. that it used force to “defend” itself (Id.). However, despite this rule may be helpful in analysis of the States’ declarations, it is usually impossible to clearly delimit between the political and legal motives of States; e.g. a State may refrain from the use of force because it is “peace-loving” or only because it decided that it is incapable to successfully conduct an intervention (M. Koskenniemi, From Apology to Utopia: The Structure of International Legal Argument (Cambridge, CUP, 2005), p. 437). As B. Stern claims, “Politics is included in the process of law creation, and the use of law, or, at least, reference to law is one of the elements of politics” (B. Stern, ‘How to Regulate Globalization?’ in M. Byers (ed.), The Role of Law in International Politics: Essays in International Relations and International Law (Oxford, OUP, 2001), p. 252). It is beyond the tasks of this article to provide a detailed account when the argumentation of States has legal character, and when it is only political. Thus, as it was mentioned, it will be generally assumed that if a State does not mention any source of law, legal norm or legal institution in its argumentation, one may assume that its reasoning is based on politics, and not on international law. Back


First, President Trump referred to the chemical attack that took place in Syria on 4 April 2017. He unequivocally declared that the regime of Syrian President Assad was responsible for this crime committed against the Syrian population. He mentioned “innocent civilians”, as well children “cruelly murdered in this very barbaric attack”. President Trump also called for “civilized nations to join us in seeking to end the slaughter and bloodshed in Syria”.

Secondly, President Trump stated that: “It is in the vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons”. However, in a further part of the statement, President Trump also mentioned the refugee crisis caused by the Middle East conflicts, which “continues to deepen and the region continues to destabilize, threatening the United States and its allies”. This suggests that the US President considered these threats to United States’ national security, as well as the security of its allies, as justifications for the strike.

Thirdly, the US President said that “Syria used banned chemical weapons, violated its obligations under the Chemical Weapons Convention, and ignored the urging of the UN Security Council”.

Apart from the President Trump’s statements, there were a few further comments on the strike on the part of the US administration. The US ambassador to the UN, Nikki Haley, claimed that “when the international community consistently fails in its duty to act collectively, there are times when States are compelled to take their own action”, and that this was true in the case of the chemical weapons attack against a civilian population. 8 Ms Haley also argued that the Syrian regime had committed crimes against humanity, which could no longer “go unanswered”. Her further statement – “It was time to say ‘enough’, but not only say it; it was time to act. Bashar Al-Assad must never use chemical weapons again, ever” – can be interpreted as suggesting that the strike was a type of punishment or retaliation for the crimes committed by President Assad’s regime. 9 As further reasons for the strike announced by President Trump, Ms Haley mentioned the breach of the UNSC resolutions, while stressing that this organ did not “move forward” due to the Russian objections, which implies that the United States was fully aware that the UNSC did not consent to the ultimate tool, i.e. collective action. Ms Haley also called for a political solution to the crisis in Syria. The only reference to the well-known criteria for the legal use of force was the claim that “The United States took a very measured step last night”, which could be interpreted as a reference to the requirement of proportionality. However, Ms Haley did not attempt to make any explicit claims about the legality of the US actions under international law. 10

In addition, the US Secretary of State, Rex W. Tillerson, pointed out that the United States had to act, since if Assad continued to use chemical weapons without any response from the international community, it could amount to “normalizing the use of chemical weapons, which may then be adopted by others”. Thus, it was “important that some action be taken on behalf of the international community to make clear that the use of chemical weapons continues to be a violation of international norms”. One may read these words that the US was afraid that further, unchallenged use of chemical weapons by

8 UNSC Provisional Records, 72nd year, 7919th meeting, 7 April 2017, S/PV.7919, p. 17. Back
9 Anticipating the further claims made in this paper, one should observe that the prohibition of the use of force includes also the prohibition of the use of punitive force, as it is the case here. The use of punitive force is usually referred to term “reprisals” which stands for “acts which are in themselves illegal and have been adopted by one state in retaliation for the commission of an earlier illegal act by another state” (M. Shaw, International Law (Cambridge, CUP, 2008), p. 1129). Some authors distinguish between legal and illegal reprisals, e.g. Y. Dinstein writes about the defensive and punitive reprisals (Y. Dinstein, Aggression and Self-defence (Cambridge, CUP, 2005, 4th ed.), p. 222). Reprisals may be of armed or non-forcible character. As to the armed reprisals, their aim may be, inter alia, to compel a State that had violated international law to comply with legal norms in the future (D. Bowett, ‘Reprisals Involving Recourse to Armed Force’, Vol. 66 American Journal of International Law 1972, p. 3). Given the statements made by the representatives of the US administration, that was the goal of the strike on the Syrian military base. Since the UN Charter allows for the unilateral use of force only for the defensive goals (N. Tsagourias, ‘Necessity and the Use of Force: A Special Regime’, Vol. 41 Netherlands Yearbook of International Law 2010, p. 26), the punitive character of armed reprisals excludes its legality under the UN Charter. Back
10 S/PV.7919, supra note 8, p. 17. Back


Syrian regime could lead to modification of customary norms or re-interpretation of treaty norms prohibiting the use of chemical weapons; thus, the aim of the US action was to uphold the position that the use of chemical agents continued to amount to the violation of international law. Secretary Tillerson also underlined that the US strike was proportional. 11 Likewise, National Security Advisor H. R. McMaster underlined the proportionality of the attack and indicated that the action was carried out in such a manner to “minimize risk to third-country nationals at that airport”. 12 On the other hand, the Secretary of Defence Jim Mattis’ comment confirmed that the US strike was in fact a police action and punishment for the President Assad’s regime, as he stated that “The Syrian government would be ill-advised ever again to use chemical weapons”, as well as that the aim of the action was to “deter future use of chemical weapons and to show the United States will not passively stand by.” 13

Summing up these statements, the US took the position that in case of inaction on the part of the UNSC, or violations of international law or the UNSC resolutions, it is allowed to use force to stop breaches of international law committed by another State and to punish this State for these violations. Such an approach is not a novelty in case of the US, but rather a continuing policy, to mention only the justification the US invoked in case of the US intervention in Iraq in 2003. 14 However, one also needs to observe that apparently, the US did not have a single, well-articulated, pre-prepared reasoning for the strike, including also a comprehensive legal argumentation, since different representatives of the US administration highlighted different grounds and aspects of the intervention.

Article 2(4), prohibiting the use of force, declares that: “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations”. The UN Charter establishes two exceptions to the prohibition to the use of force, while only one of them allows for the unilateral use of force, that is the right to self-defence, which is regulated in Article 51 of the UN Charter. Bearing in mind the content of these Charter provisions, one may presume that the strike conducted by the United States was unlawful, since it did not constitute self-defence as defined in Article 51 of the UN Charter, and as a result the US breached the prohibition of the use of force. However, given that throughout the last 72 years States have used force for different reasons, exceeding the legal framework of the lawful right to self-defence, one needs to analyse the justification provided by President Trump and other US representatives, in light of the practice of States and the current state of international law, including also the state of CIL. Thus, this part of the article examines the legality of the strike bearing in mind the statements made by the US administration.

1. Humanitarian Grounds

Even though President Trump did not use the term “humanitarian intervention” as the legal grounds for the strike conducted by the US, he clearly referred to “humanitarian reasons” by mentioning the “killing of innocent civilians” and the “barbaric attack”. Could these be legal grounds for the US strike?

Despite many claims in the doctrine of international law that have qualified different interventions as humanitarian ones, 15 since the adoption of the UN Charter only two States, namely, the United Kingdom and Belgium, explicitly justified the use of force as a humanitarian intervention. With respect to NATO’s

11 ‘Remarks with National Security Advisor H.R. McMaster’, 6 April 2017, Back
12 Id. Back
13 Statement by Secretary of Defense Jim Mattis on the U.S. Military Response to the Syrian Government’s Use of Chemical Weapons’, 10 April 2017, Back
14 UNSC Provisional Records, 58th year, 4701st meeting, 5 February 2003, S/PV.4701, p. 2–17. Back
15 For instance, some authors point out that the intervention carried out by India in Pakistan in 1971, Vietnam’s intervention in Cambodia in 1978, the intervention of the coalition of States in Iraq in 1991, or the Tanzania’s intervention in Uganda in 1979, constituted “classical” examples of humanitarian intervention (e.g. G. R. Lucas, ‘The Role of the “International Community” in Just War Tradition – Confronting the Challenges of Humanitarian Intervention and Preemptive War’, Vol. 2 no. 2 Journal of Military Ethics 2003, p. 127; O. A. Hathaway, J. Brower, R. Liss, T. Thomas & J. Victor, ‘Consent-Based Humanitarian Intervention: Giving Sovereign Responsibility Back to the Sovereign’, Vol. 46 Cornell International Law Journal 2013, p. 510), while these conclusions are not confirmed by the statements made by States. Back


armed intervention in Kosovo, including Belgium’s participation, Belgium presented its arguments during the proceedings before the International Court of Justice (ICJ), arguing in the case on the legality of use of force launched against Belgium by the Federal Republic of Yugoslavia (thereafter Serbia and Montenegro). 16 In justifying the NATO operation in Kosovo, the representatives of Belgium made a clear reference to the “idea of an armed humanitarian intervention”, and claimed that “NATO, and the Kingdom of Belgium in particular, felt obliged to intervene to forestall an ongoing humanitarian catastrophe, acknowledged in Security Council resolutions”. Thus, Belgium wanted to safeguard “values” that have the rank of jus cogens norms, such as the right to life, physical integrity, and the prohibition of torture. It presented an interpretation of Article 2(4) of the UN Charter, according to which Article 2(4) prohibits the use of force only against the territorial integrity or political independence of a State; thus humanitarian interventions, having different goals, are compatible with the provisions of Article 2(4) of the UN Charter. Belgium also defined three criteria of a lawful humanitarian intervention (allegedly asserted by the UNSC, although Belgium did not refer to any particular document to support such a claim): a humanitarian catastrophe recognized by the UNSC; imminent danger, i.e. a situation constituting a threat to peace, recognized as such in a UNSC resolution; and a power responsible for this catastrophe. However, despite such strong claims and elaborate argumentation, Belgium decided to refer “alternatively” to the state of necessity as the justification of the NATO intervention in the event it failed to convince the Court that the armed humanitarian intervention was justified under international law. 17 No other State 18 ever referred to these statements and attempted to use these claims to justify the legality of a humanitarian intervention.

Moreover, it is worthwhile to note that a few years before the intervention in Kosovo, Belgium supported an operation conducted under quite similar circumstances, that is the operation “Provide Comfort” in Iraq in 1991. M. Eyskens, the Belgian Minister of Foreign Affairs at that time, indicated in his address to the Belgium parliament that the international community had to help the Kurdish population in Iraq; however, if there were no legal regulations which could constitute the basis for the military intervention, States would have to create such legal grounds on an ad hoc basis. Moreover, Mr. Eyskens already in 1991 considered the humanitarian intervention as the reasons for an armed intervention; however, he did not explicitly claim that general international law allows for such an action. He considered Common Article 3 of the Geneva Conventions as the grounds for the intervention, but in the end he came to the conclusion that this provision does not legitimize a humanitarian intervention. As a result, he concluded that Belgium would interpret paragraph five of the UNSC Resolution 688 as allowing for the humanitarian intervention. 19 He also suggested that Belgium would support the intervention in Iraq, even if such intervention was not authorized by the UNSC. 20

The other State whose position in relation to the concept of a humanitarian intervention should be mentioned is the United Kingdom, who also issued statements on the humanitarian grounds of the intervention in Kosovo. During the debate in the UNSC, the representative of the United Kingdom claimed that the intervention in Kosovo “is justified as an exceptional measure to prevent an

16 Similar proceedings were launched also against Canada, France, Germany, Italy, Netherlands, Portugal, Spain, the United Kingdom and the United States. Back
17 Legality of Use of Force (Serbia and Montenegro v. Belgium) , Public sitting held on Monday 10 May 1999, at 3 pm, at the Peace Palace, Vice-President Weeramantry, Acting President, presiding, CR 1999/15. As to the state of necessity, it is noteworthy to observe that States tend to justify the humanitarian intervention by the state of necessity, especially since there is no clear legal basis for humanitarian intervention in international law nowadays (Tsagourias, supra note 9, pp. 23–24). Back
18 Likewise, the ICJ claimed that it had no jurisdiction to entertain all the claims made by Serbia and Montenegro; Application filed by Serbia and Montenegro on 29 April 1999 (Legality of Use of Force (Serbia and Montenegro v. Belgium) , 15 December 2004, Preliminary Objections, Judgment, I.C.J. Reports 2004, p. 279, § 129. Back
19 “[…] also requests the Secretary-General to use all the resources at his disposal, including those of the relevant United Nations agencies, to address urgently the critical needs of the refugees and displaced Iraqi population”. (UNSC Res. 688, 5 April 1991). Back
20 Cited in Annales parlamentaires, Sénat, 17 avril 1991, pp. 1994-1995 [in:] A. Daemes, ‘Absence de Base Juridique de l'Operation Provide Comfort et la Practique Belge en Matiere d'Intervention Armee à But Humanitaire’, Vol. XXV Issue 1 Revue Belge de Droit International 1992, pp. 266–267. Back


overwhelming humanitarian catastrophe”. 21He also indicated the criteria of the legality of the intervention, such as the imminence of the “overwhelming humanitarian catastrophe”, the exhaustion of non-forcible measures, and the use of force exclusively to avert a humanitarian catastrophe. 22

However, with reference to the United Kingdom one should also invoke the advice offered concerning the legality of war with Iraq by the attorney general, Lord Goldsmith, to British prime minister Tony Blair right before operation “Iraqi Freedom” was launched in March 2003. Lord Goldsmith claimed that there are three grounds for the legal use of force in general: self-defence, “exceptionally, to avert an overwhelming humanitarian catastrophe”, as well as “authorization by the Security Council acting under Chapter VII of the UN Charter”. 23As to this second ground, he stated that:
[t]he use of force to avert an overwhelming humanitarian catastrophe has been emerging as a further, and exceptional, basis for the use of force. It was relied on by the UK in the Kosovo crisis and is the underlying justification for the No-Fly Zones. The doctrine remains controversial, however. I know of no reason why it would be an appropriate basis for action in the present circumstances. 24
The same conclusion was also reached in the Fourth Report of the Committee on Foreign Affairs of the House of Commons, which made it clear that “the doctrine of humanitarian intervention has a tenuous basis in current CIL, and that this renders the NATO action legally questionable”. 25 In the end, humanitarian reasons were not invoked as the grounds for the operation in Iraq in 2003.

It is also worth noting that while the United States has mentioned humanitarian grounds three times since 1945 as a basis for using force, it never attempted to use the humanitarian crisis as the principal legal grounds for its intervention, since it always constituted only an additional argument in favour of the intervention – one which was in the background of strong legal argumentation. The first such operation occurred in 1963, when the United States intervened in the Dominican Republic. Apart from the alleged consent of the Dominican authorities 26 and the support received from the OAS, 27 the United States, invoked, inter alia, 28 humanitarian grounds. The US Ambassador to the UN claimed in the UNSC that before the US intervention began, the Red Cross estimated that there were about 400 causalities from the internal strife in the Dominican Republic, that hospitals could not cope with saving those who were wounded, and in addition there were shortages of medicines, food, and power supplies. 29

The second time the United States mentioned humanitarian grounds as a basis for using force was in April 1980, when the US tried to free the American citizens taken as hostages in the US Embassy in Tehran, and the operation failed due to a collision between American aircrafts. 30 In the aftermath of this failure, President Carter addressed the nation in a TV speech, wherein he claimed that the operation was supposed to be a “humanitarian mission”. 31 However, above all, President Carter was clearly trying to calm down the Iranian authorities, claiming, inter alia, that the attempted intervention “was not directed

21 UNSC Provisional Record, 54th year, 3988th meeting, 24 March 1999, S/PV.3988, p. 12. Back
22 Id. Back
23 Full text of the advice about the legality of war with Iraq given by the attorney general, Lord Goldsmith, to the prime minister, Tony Blair, on March 7, 2003, § 2, Back
24 Id., § 4. Back
25 House of Commons, Foreign Affairs – Fourth Report. International Law, Session 1999-2000, § 132. Back
26 L. Doswald-Beck, ‘The Legality of Military Intervention by Invitation of the Government’, Vol. 56 Issue 1 B.Y.I.L. 1985, p. 228. a href="#fn26-rf">Back
27 N. T. D. Kanakaratne, ‘US Intervention and the UN Charter’, Vol. 24 Guild Practitioner 1965, pp. 107–108. Back
28 The US further claimed that their nationals (as well as other foreigners) were endangered, as well as that the communists could take over the control in Dominican Republic (‘U.S. Acts to Meet Threat in Dominican Republic. Statement by U.S. Representative, April 28’, Vol. LII No. 1338 Department of State Bulletin January 4, 1965, p. 740; Letter dated 29 April 1965 from the Permanent Representative of the United States of America Addressed to the President of the Security Council/ Presidential Statement on the Dominican Situation, issued at 9 pm, 28 April 1965, S/6310; K. R. Schmeltzer, ‘Soviet and American Attitudes Toward Intervention: The Dominican Republic, Hungary and Czechoslovakia’, Vol. 11 Virginia Journal of International Law 1970-1971, p. 105). Back
29 UNSC Official Records, 20th year, 1196th meeting, 3 May 1965, S/PV.1196, § 67–68. Back
30 J. Eldred, ‘The Use of Force in Hostage Rescue Missions’, Vol. 56 Naval Law Review 2008, p. 266. Back
31 Jimmy Carter, ‘Address to the Nation on the Rescue Attempt for American Hostages in Iran’, 25 April 1980, Back


against Iran; it was not directed against the people of Iran”. In the end the United States referred to the right to self-defence, and under Article 51 of the UN Charter reported the use of force to the UNSC, using President’s Carter address as the official justification for the operation. 32

In the third such instance, the United States also used such terms as “a mission of mercy” and a “humanitarian mission” 33 when justifying its support for the Belgian operation in Congo in 1964, when the US provided the transport to evacuate the hostages freed by the Belgian forces. However, in this instance it was not the United States which employed its troops in Congo, so in the end it was Belgium that had to find a legal justification for the operation (the principal one was the consent for the intervention granted by the Prime Minister of Congo, Moïse Tshombe). 34

Bearing in mind these three examples, 35 one may conclude that historically the United States has not been willing to refer to humanitarian grounds to justify a use of force, and in the instances where they did so, alongside such “humanitarian” arguments they also invoked other legal bases for intervention, more solid and less controversial under international law.

Moreover, the United States has also been reluctant to support other States when they used such “humanitarian” grounds to justify the use of force. When India invoked the persecutions of the population of Bangladesh, together with the right to self-defence, during its intervention in Pakistan in 1971, the United States did not openly condemn India, but “declared as unacceptable a situation in which a government intervened across its borders in the affairs of another with military force in violation of the Charter”. 36 It is also worth noting that the United States was also one of the first States to report to the UN Secretary-General the situation in Kampuchea and the genocide committed by the Pol Pot regime against its own nationals in 1977. 37 However, despite designating the crimes committed then as the gravest ones since the Nazi times, 38 the US did not suggest an intervention (nor did any other State).

32 Letter Dated 25 April 1980 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security Council, S/13908. Back
33 Letter dated 24 November 1964 from the Permanent Representative of the United States of America Addressed to the President of the Security Council – Letter from the Prime Minister of the Democratic Republic of the Congo to the American Ambassador in Leopoldville, 21 November 1964 – Statement of the United State Governmen t, S/6062, pp. 1– 2. Back
34 H. I. Weisberg, ‘The Congo Crisis 1964: A Case Study in Humanitarian Intervention’, Vol. 12 Vanderbilt Journal of International Law 1971-1972, p. 263; Letter Dated 24 November 1964 from the Permanent Representative of Belgium Addressed to the President of the Security Council/ Letter Dated 21 November 1964 Addressed to Count de Kerchove de Denterghem, Ambassador of Belgium at Leopoldville/ Statement by Mr. P.H. Spaak, Minister of Foreign Affairs of Belgium, on 24 November 1964, S/6063, p. 3. Tshombe was overthrown by Christopher Gbenye, but the latter did not form a government with effective control over the whole territory of the State. Back
35 One could also invoke a fourth example when it comes to the statements of the US officials on humanitarian reasons behind armed interventions, i.e. the US intervention in Grenada in 1983. To justify that operation, the United States officially invoked three grounds: action within the framework of a regional organization (the Organization of Eastern Caribbean States reportedly deemed the situation in Grenada as a threat to the peace and security of the Caribbean States and asked the United States for help) (Letter dated 25 October 1983 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security Council, S/16076); protection of American citizens (‘Ambassador Kirkpatrick’s Statement, UN Security Council, Oct. 27, 1983’, Vol. 83 2061 Department of State Bulletin December 1983, p. 75); as well as the need to restore the order and security in Grenade since the situation in that State constituted the threat to international peace and security (Letter dated 25 October 1983 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security Council, S/16076). However, apart from this official approach one should also refer to the statement of the Legal Advisor of the US Department of State, David R. Robinson, made in a letter addressed to Professor Edward Gordon, dated 10 February 1984, where he referred to the doctrine of humanitarian intervention, claiming that it could not be invoked as the grounds of the American intervention (‘Letter from the Legal Advisor’, United States Department of State, Vol. 18 International Lawyer 1974, pp. 382–386). Back
36 ‘Situation in the India/Pakistan Subcontinent, Initial Proceedings’, Repertoire of the Practice of the Security Council, 1969-1971, Chapter VIII, p. 156. Back
37 ‘Submission from the Government of the United States of America under Commission on Human Rights decision 9 (XXXIV)’, E/CN.4/Sub.2/414/Add.4. Back
38 M. L. Bazyler, ‘Reexamining the Doctrine of Humanitarian Intervention in Light of the Atrocities in Kampuchea and Ethiopia’, Vol. 23 Stanford Journal of International Law 1987, p. 552. Back


Undoubtedly, the concept of a humanitarian intervention is a broad and complex topic, and has been discussed in countless publications. 39 Different authors have presented opposing opinions and various arguments in favour of their views. The aim of this article however is not to present this discussion, but to examine States’ practice. Bearing in mind the fact that since 1945 no State has invoked a humanitarian intervention as the sole legal basis for their unilateral intervention, one can assume that the concept of a “humanitarian intervention”, in other words an intervention conducted for humanitarian reasons, regardless of its name has not been viewed by the international community as the legal basis for any action since 1945. Only two States out of 193 40 have referred to humanitarian grounds for a military intervention, only in reference to collective operations, and moreover one of these States received negative feedback on the legality of the humanitarian intervention from its own legal advisors. These are the approaches adopted by States that principally count when it comes to the interpretation of treaties and the formation of CIL. Having examined this practice and States’ views, it should be concluded that intervention for humanitarian reasons is not another exception to the prohibition of the use of force. This standpoint has been, until now, confirmed also by the United States. Under these circumstances, the reference by the United States to the humanitarian situation in Syria as one of the principal arguments is, without any other firm justification, unique and non-tenable. 41

2. The Vital Security Interests of the United States and its Allies

The second justification for the strike invoked by President Trump was based on the “vital national security interests” of both the United States and its allies, “to prevent and deter” future threats coming from the spread and use of the chemical weapons, as well as the refugee crisis. A few references to international legal institutions are reflected here, but nevertheless none of them are well-grounded and could justify the use of force.

First of all, before discussing in details this part of the US claims, one needs to refer to the protection of “vital national security interests”, as invoked by President Trump. The ICJ in Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda) had to the deal with Uganda’s

39 To list just a few papers that refer specifically to the so-called ‘humanitarian intervention’: M. Akehurst, ‘Humanitarian Intervention’, in H. Bull (ed.), Intervention in World Politics (Oxford, OUP, 1984); A. C. Arend & C. C. Joyner, ‘Anticipatory Humanitarian Intervention as an Emerging Legal Norm’, Vol. 10 United States Air Force Academy of Journal of Legal Studies 1999-2000; R. B. Lillich, Humanitarian Intervention and the United Nations (Charlottesville, University Press of Virginia, 1973); A. Cassese, ‘A Follow-Up: Forcible Humanitarian Countermeasures and Opinio Necessitatis’, Vol. 10 No. 4 European Journal of International Law 1999; J. Pattison (ed.), Humanitarian Intervention. Volume III: The Ethical Issue Surrounding Humanitarian Intervention (Los Angeles/ London/New Delhi/ Singapore/ Washington, Sage, 2014); T. M. Franck & N. S. Rodley, ‘After Bangladesh: The Law of Humanitarian Intervention by Military Force’, Vol. 67 American Journal International Law 1973; J. Moore (ed.), Hard Choices. Moral Dilemmas in Humanitarian Intervention (Lanham/Boulder/New York/ Toronto/ Oxford, Rowman & Littlefield Publishers, 1999); L. Henkin, ‘Humanitarian Intervention’, Vol. 26 Studies in Transnational Legal Policy 1994; J. Trahan, ‘Defining the “Grey Area” Where Humanitarian Intervention May Not Be Fully Legal, But is Not the Crime of Aggression’, Vol. 2 No. 1 Journal on the Use of Force and International Law 2015; and W. D. Verwey, ‘Humanitarian Intervention’, in A. Cassese, supra note 5). Back
40 Currently 193 States are the UN Member States. Back
41 In this respect, one should also observe that the President Trump’s claims about the legality of the strike due to the crimes committed by President Assad against its own citizens, can be interpreted in the context of the “Responsibility to Protect”. This doctrine, announced by the International Commission on Intervention and State Sovereignty in the 2001 Report, postulates that that every sovereign State is responsible for the protection of its own citizens from avoidable catastrophes, like e.g. from mass murders; however, if a State is unwilling or unable to do so, that responsibility shifts to the international community (International Commission on Intervention and State Responsibility, ‘The Responsibility to Protect. Report of the International Commission on Intervention and State Responsibility’, p. viii, Consequently, the doctrine allows, in “extreme cases”, for an armed intervention in a State that fails to protect its citizens ( Id., §§ 1.37, 4.1, 4.34.). Moreover, the Report does not exclude the unilateral interventions in such cases, neither requires the authorization on the part of the UNSC. Even though none of the US representatives referred to the "Responsibility to Protect", it is noteworthy to observe that such shape of this doctrine, as presented in the 2001 Report, is in contravention with the UN Charter since it establishes an additional exception to the prohibition to the use of force. However, the doctrine was accommodated by the UN, since, as pointed out in the 2005 World Summit Outcome, “we are prepared to take collective action, in a timely and decisive manner, through the Security Council, in accordance with the Charter, including Chapter VII, on a case-by-case basis and in cooperation with relevant regional organizations as appropriate, should peaceful means be inadequate and national authorities are manifestly failing to protect their populations from genocide, war crimes, ethnic cleansing and crimes against humanity” (UNGA Res. 60/1, 24 October 2005, § 139.). As a result, the UN recognized the doctrine, but only as a part of the collective security system. It may serve as another argument against the legality of the US strike. Back


claim that Uganda Peoples’ Defence Forces were carrying out the operation “Safe Haven” on the territory of the Democratic Republic of Congo (DRC) to protect “Uganda’s legitimate security interests.” The Court observed that the Ugandan High Command’s document that provided the basis for the “Safe Haven” operation referred to the Uganda’s security needs that were “essentially preventative”, and, despite its claims, Uganda neither reported to the UNSC that it had been acting in self-defence, nor ever claimed that it had been subjected to an armed attack conducted by the DRC armed forces. Thus, as the Court concluded:
Article 51 of the Charter may justify a use of force in self-defence only within the strict confines there laid down. It does not allow the use of force by a State to protect perceived security interests beyond these parameters. Other means are available to a concerned State, including, in particular, recourse to the Security Council. 42
To sum up, the ICJ unequivocally stated that the use of force for the protection of security interests cannot be the legal grounds for the use of force, unless a State invoked the right to self-defence, since the requirements of Article 51 were met. Bearing in mind the statement made by President Trump, this argument suffices to say that, without the fulfilment of the conditions of the right to self-defence, the US operation was not lawful, if based only on “vital security interests”. 43

This evaluation of the lawfulness of the US strike is not changed by the further examination of the President Trump’s words. The need to “prevent and deter” is related to one of the most recent American military doctrines, i.e. the one promoted by the administration of President G. W. Bush. Article 51 of the UN Charter explicitly allows for self-defence “if an armed attack occurs”, which means that a State is entitled to the right to self-defence only when it was previously attacked, not prior thereto. 44 Nevertheless, since Article 51 of the UN Charter also refers to the “inherent right of individual or collective self-defence”, some authors claim that it allows also for anticipatory self-defence. 45 This term

42 ICJ, Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v. Uganda) , 19 December 2005, I.C.J. Rep 2005, p. 168, §§ 109, 143, 146, 148. Back
43 President Trump’s claims may be referred also to another ICJ’s case, namely the Corfu Chanel case. The United Kingdom claimed that the operation of minesweeping was “a new and special application of the theory of intervention, by means of which the State intervening would secure possession of evidence in the territory of another State, in order to submit it to an international tribunal and thus facilitate its task”. However, the Court found that this “alleged right of intervention” is in fact “the manifestation of a policy of force, such as has, in the past, given rise to most serious abuses and such as cannot, whatever be the present defects in international organization, find a place in international law” (ICJ, Corfu Channel Case (UK v. Albania), 9 April 1949, I.C.J. Rep. 1949, p. 22, 31). Thus, the lack of effectivity of the international organizations does not allow States to use, or to manifest, force. Back
44 Authors who support this view include: A. Abass & N. D. White, ‘Countermeasures and Sanctions’, in M. D. Evans, International Law (Oxford, OUP, 2003), p. 506; D. A. Sadoff, ‘A Question of Determinacy: The Legal Status of Anticipatory Self-Defense’, Vol. 40 Georgetown Journal of International Law 2008-2009, pp. 541, 552; D. Armstrong, T. Farrell & H. Lambert, International Law and International Relations (Cambridge, CUP, 2012), pp. 135-136; Akehurst, supra note 39, p. 107; Joyner & Arend, supra note 39, p. 34; L. Henkin, How Nations Behave. Law and Foreign Policy (New York, Columbia University Press, 1979), p. 141; I. Brownlie, International Law and the Use of Force by States (Oxford, OUP, 1963), p. 278; J. Žourek, L’Interdiction de l’emploi de la Force en Droit international (Genève, Institute Henri Dunant, 1974), p. 101; Hillier, supra note 4, p. 605; A. Cassese, ‘Return to Westphalia? Considerations on the Gradual Erosion of the Charter System’ in Cassese (ed.), supra note 5, p. 516; Q. Wright, ‘The Prevention of Aggression’, Vol. 50 The American Journal of International Law 1956, p. 529; R. Värk, ‘The Use of Force in the Modern World: Recent Developments and Legal Regulation of the Use of Force’, Vol. 2 No. 10 Baltic Defence Review 2003, p. 36; M. J. Glennon, ‘The Fog of Law: Self-Defense, Inherence, and Incoherence in Article 51 of the United Nations Charter’, Vol. 25 Harvard Journal of Law & Public Policy 2001-2002, p. 546; p. 45; J.T. Gathii, ‘Assessing Claims of a New Doctrine of Pre-emptive War Under the Doctrine of Sources’, Vol. 43 No. 1 & 2 Osgoode Hall Law Journal 2005, p. 73; A. A. C. Trindade, ‘The Primacy of International Law over Force’, in M. G. Kohen (ed.), Promoting Justice, Human Rights And Conflict Resolution Through International Law (Geneva, Brill, 2007), p. 1045; and R. W. Tucker, ‘The Interpretation of War Under Present International Law’, Vol. 4 The International Law Quarterly 1951, p. 29. Back
45 Gordon, supra note 4, p. 125; G. Simpson, ‘Law and Force in the Twenty-First Century’ in D. Armstrong (ed.), Routledge Handbook of International Law (Abingdon, Routledge, 2009), p. 203; M. C. Alder, The Inherent Right of Self-Defence in International Law (Dordrecht, Springer, 2013), p. 88; Hillier, supra note 4, p. 605; Sadoff, supra note 34, p. 535; A. S. Weiner, ‘The Use of Force and Contemporary Security Threats Old Medicine for New Ills’, Vol. 59 Issue 2 Stanford Law Review 2006, p. 423. However, there are also other arguments which support the view that anticipatory self-defense is permissible on the grounds of the UN Charter, that is: the Charter’s preparatory works (T. M. Franck, ‘Who Killed Article 2(4) or: Changing Norms Governing the Use of Force by States’, Vol. 64 American Journal of International Law 1970, p. 821); the fact that it is the State which discretionally decides whether the circumstances require self-defense (H. Kelsen, ‘Collective Security and Collective Self-Defense Under the Charter of the United Nations’, Vol. 42 No. 4 American journal of International Law 1948, p. 791); and the less restrictive wording of the French text of the Charter (R. Higgins, The Development of International Law Through the Political Organs of the United Nations (Oxford, OUP, 1963), p. 199). Back


refers to the use of force in self-defence when an armed attack has not occurred yet, but the threat of such an attack is imminent, as well as when the State has no other means to prevent the attack. 46 Without prejudice to whether this position is justified on the grounds of the UN Charter, after the 9/11 attacks the United States began to claim that self-defence is allowed not only when an armed attack has already occurred or is imminent, but also when the threat of an armed attack is still remote, and the threat is connected with global terrorism and the proliferation of weapons of mass destruction; 47 this latter concept is usually referred to as pre-emptive or preventive self-defence. 48

These claims were included first and foremost in the 2002 US National Security Strategy which stated, inter alia, that: “We must deter and defend against the threat before it is unleashed”; “(…) deterrence based only upon the threat of retaliation is less likely to work against leaders of rogue states more willing to take risks”; “our military must (..) deter threats against U.S. interests, allies, and friends”; “the United States will (…) strengthen alliances to (…) prevent our enemies from threatening us, our allies, and our friends, with weapons of mass destruction”; as well as that “we will not hesitate to act alone, if necessary, to exercise our right of self-defence by acting pre-emptively against such terrorists, to prevent them from doing harm against our people and our country”. 49 Consequently, this so-called “Bush doctrine” 50 claimed that the United States was allowed to act pre-emptively, by way of deterrence and prevention. Pre-emptive also means included military intervention to protect itself and US allies against the threats on the part of terrorism and those who possess weapons of mass destruction. International law scholars, and especially American authors, were divided as to the legality of the doctrine (probably the best summary of this was presented by C. Henderson, who pointed out that some States and commentators were willing to accept the idea of pre-emptive use of force “if it was used multilaterally and evoked the ideals of collective security”, but not as an authorization for unilateral action, as proposed by the United States). 51 However, despite the clear connotations between the Bush Doctrine and the justification of the strike against a military base in Syria presented by President Trump, one needs to underline that President Trump did not mention self-defence, whether anticipatory or pre-emptive, at all, but referred only to the need to “prevent and deter”. Thus, even if the concepts of national security presented by Presidents Trump and Bush are close in substance, the former does not refer to any legal institutions at all. 52 Thus, regardless of whether the “Bush doctrine” is acceptable under international law or not, the

42 D. Švarc, ‘Redefining Imminence: the Use of Force Against Threats and Armed Attacks in the Twenty-First Century’, Vol. 13 ILSA Journal of International & Comparative Law 2006-2007, p. 173; E. Wilmshurst, ‘The Chatham House Principles of International Law on the Use of Force in Self-Defence’, Vol. 55 No. 4 The International and Comparative Law Quarterly 2006, p. 964; T. Bakken, ‘Nations’ Use of Force Outside Self-Defense’, Vol. 8 Georgetown Journal of Law & Public Policy 2010, p. 453; Värk, supra note 44, pp. 35–38; G. M. Reichberg, ‘Preventive War in Classical Just War Theory’, Vol. 9 Journal of the History of International Law 2007, pp. 6–7; K. Slager, ‘Legality, Legitimacy and Anticipatory Self-Defense: Considering an Israeli Preemptive Strike on Iran’s Nuclear Program’, North Carolina Journal of International Law & Commercial Regulation 2012-2013, p. 289; and T. M. Franck, ‘Preemption, Prevention and Anticipatory Self-Defense: New Law Regarding Recourse to Force?’, Vol. 27 No. 3 Hastings International and Comparative Law Review 2004, p. 426. Back
47 C. Henderson, ‘The Bush Doctrine: From Theory to Practice’, Vol. 9 No 1. Journal of Conflict & Security Law 2004, pp. 5–6. Back
48 A. D. Sofaer, ‘On the Necessity of Pre-emption’, Vol. 14 European Journal of International Law 2003, pp. 221–225; Švarc, supra note 46, p. 173. Back
49 The National Security Strategy of the United States of America, September 2002, Back
50 Among rich scholarship, one may enumerate e.g. J. Yoo, R. J. Delahunty, ‘The Bush Doctrine: Can Preventive War Be Justified’, Vol. 32 Issue 3 Harvard Journal of Law & Public Policy 2009, pp. 843–866; J. R. Paul, ‘The Bush Doctrine: Making or Breaking Customary International Law’, Vol. 27 Issue 3 Hastings International and Comparative Law Review 2004, pp. 457–480; C. Gray, ‘The US National Security Strategy and the New Bush Doctrine on Preemptive Self-defense’, Vol. 1 Issue 2 Chinese Journal of International Law 2002, pp. 437–448; P. F. Diehl, S. Kulkami & A. Irish, ‘The Bush Doctrine and the Use of Force: Reflections on Rule Construction and Application’, Vol. 9 Issue 1 Loyola University Chicago International Law Review 2011, pp. 71–102; and M. Buckley & R. Singh, The Bush Doctrine and the War on Terrorism: Global Responses, Global Consequences (London, Routledge, 2006). Back
51 Henderson, supra note 47, p. 12. Back
52 When it comes to the use of force in case of the employment of the weapons of mass destruction, one should also refer to the so called “Obama doctrine”, which claimed in 2012 that if the Assad regime used chemical weapons against civilians, it would cross the “red line” and thus, it would trigger the US military intervention (‘Remarks by the President to the White House Press Corps’, 20 August 2012, President Obama never justified this concept by reference to international law; however, it soon turned out that such justifications were not needed since in fact the US administration did not plan any intervention. A year later, when Assad became engaged in chemical weapons attacks against civilians, as reported by the media, President Obama had to “erase” the “red line” (B. Wolfgang, ‘Obama ‘Red Line’ Erased as Bashar Assad’s Chemical Weapons Use Goes Unchecked by U.S. Military’, 17 May 2015, Back


reason for the strike presented by President Trump is not even close to an attempt to justify the armed intervention under the aegis of the “Bush doctrine”.

When it comes to the threat posed by refugees, it should be noted that it was invoked at least twice as the grounds (or one of the grounds) for a military intervention. The first of these interventions occurred in 1971 when India intervened in Pakistan. Apart from the humanitarian reasons, India invoked first and foremost the right to self-defence. However, India claimed that the self-defence was justified because of two types of actions directed against it. In the first instance India referred to the military clashes on the border with Pakistan; however, it also claimed that self-defence was justified because of the occurrence of so-called “refugee aggression”. The notion of “refugee aggression” was defined as the “disruption of India’s social and economic structure through an influx of refugees, and then through military aggression”. 53 A majority of States did not support these arguments during the debate in the UNSC 54 (however, neither the draft UNSC Resolution, vetoed by the USSR, nor the resolution adopted by the United Nations General Assembly (UN GA) condemned India; rather they urged both India and Pakistan to seek a peaceful resolution of the conflict). 55

The second time a refugee crisis was deemed as the threat to international peace and security occurred during the crisis in Iraq involving the Kurdish population in 1991. The influx of Kurdish refugees affected mostly Turkey and Iran, which warned the UN organs about the dramatic situation, with hundreds of thousands of people waiting at their borders. 56 Turkey underscored that it did not intend to interfere in the internal affairs of Iraq, but that the methods used by the Iraqi authorities against the Kurds affected the security of Iraq’s neighbours. Iran also underlined that the influx of refugees:
has added another international dimension to the crisis inside Iraq, threatening the security of the neighbouring countries and presenting the potential to further destabilize inter-State relations in our region. 57
While it is true that such States as Yemen, Cuba and Zimbabwe claimed that the humanitarian crisis was the internal matter of Iraq, and even the demands for dialogue between the conflicted groups within that State infringed Article 2(7) of the UN Charter, 58 a majority of States supported UNSC Resolution 688, which condemned the persecutions against civilians in Iraq and stated that their consequences threatened international peace and security in the region (§ 1). Moreover, even though Resolution 688 did not explicitly authorize the use of force, it provided the grounds for operation “Provide Comfort”.

Summing up, even though an influx of refugees could be recognized as a threat to international peace and security, it has never constituted independent grounds for a unilateral military intervention: India invoked right to self-defence, while in the case of the intervention in Iraq the coalition of States referred

53 Situation in the India/Pakistan Subcontinent, supra note 36, p. 156. Back
54 UNSC Official Records, 26th year, 1607th meeting, 5 December 1971, S/PV.1607; UNSC Official Records, 26th year, 1608th meeting, 6 December 1971, S/PV.1608; UNSC Official Records, 26th year, 1606th meeting, 4 December 1971, S/PV.1606. Back
55 T. M. Franck, Recourse to Force. State Action Against Threats and Armed Attacks (Cambridge, CUP, 2002), pp. 141–142; UNGA Res. 2793 (1971), 7 December 1971. Back
56 Letter dated 3 April 1991 from the Permanent Representative of the Islamic Republic of Iran to the United Nations Addressed to the Secretary-General, S/22436; Letter dated 4 April 1991 from the Permanent Representative of the Islamic Republic of Iran to the United Nations Addressed to the Secretary-General, S/22447; Letter dated 2 April 1991 from the Permanent Representative of Turkey to the United Nations Addressed to the President of the Security Council, S/22435. Back
57 UNSC Provisional Records, 2982nd meeting, 5 April 1991, S/PV.2982, pp. 8, 12–15. Back
58 Id., pp. 26–45. Back


to the UNSC resolution. Consequently, the refugee crisis, which in addition does not directly affect the United States and occurs far away from its borders, cannot be the grounds for the action undertaken. 59

Consequently, neither the “vital security interests”, nor the need to “prevent and deter”, nor the threats posed by the refugee crisis, allow States to unilaterally use force under public international law.

3. The Chemical Weapons Convention and UNSC Resolutions

The third basis for the strike invoked by President Trump referred to the breach of the Chemical Weapons Convention, 60 as well as the Syrian regime ignoring “the urging of the U.N. Security Council”.

Firstly, one needs to analyse whether the Chemical Weapons Conventions allows for the use of force in the event of a breach of its provisions. In this respect, one needs to start from the Convention’s Preamble, which states, inter alia, that the aim of the Convention is to “contribute to the realization of the purposes and principles of the Charter of the United Nations”. Since among the purposes of the UN is to “maintain international peace and security” (Article 1(1)), while the prohibition of the use of force is one of the main principles of the Organization (Article 2(4)), it seems clear that the Convention itself should contribute to international peace and security. However, given that one may interpret this reference as granting the organs established under the Convention some special powers to effect the “realization of the purposes and principles of the Charter”, one should bear in mind that it is the UNSC which has “primary responsibility for the maintenance of international peace and security” (Article 24(1)), and nothing in the preamble suggests that the organs formed under the Convention share the UNSC competences.

One should further refer to Article XII of the Convention, which regulates “measures to redress a situation and to ensure compliance, including sanctions”. Paragraph three of this Article provides that: “In cases where serious damage to the object and purpose of this Convention may result from activities prohibited under this Convention, in particular by Article I, the Conference may recommend collective measures to States Parties in conformity with international law”. To “recommend” means that the proposal submitted by the Conference of State Parties 61 is not legally binding. Moreover, “conformity with international law” refers, inter alia, again to the prohibition of the use of force and the competences of the UNSC, which cannot be infringed upon by the actions undertaken by the Organization for the Prohibition of Chemical Weapons (OPCW). Thus, the Conference may recommend only such “collective measures” as to refrain from the production or export of chemicals, technical facilities or know-how. Despite this, G. den Dekker does not exclude the possibility that, in case of an armed attack, as stated in Article 51 of the UN Charter, with the use of chemical weapons, the Conference could also recommend collective self-defence. 62 However, the OPWC is not a defence pact. Moreover, while paragraph three allows for collective measures in cases of “serious damage to the object and purpose of this Convention”, paragraph four concerns much more serious situations, that is “cases of particular gravity”, and an armed attack should definitely be qualified as the latter. Thus, when a “case of particular gravity” occurs, it is no longer the Conference which is to make recommendations, but rather it is obliged (“shall”) inform the UN GA or the UNSC about the situation. As a result, in the end it is the UNSC which may consider a breach of the Convention as a threat to international peace and apply appropriate measures, 63 including the use of force.

Bearing in mind the above, the Chemical Weapons Convention does not allow any of the organs of the OPCW to authorize the use of force in a case involving the use of chemical weapons. Even more, the

59 However, even if to assume that the US understands its “security interests” in a broader sense, including also “security interests” of its allies, none of the European allies of the US claimed that the refugee crises constituted the threat to the international peace and security or an armed attack (in the sense of the so called ‘refugee aggression’) etc. Back
60 The full name of the Convention is the ‘Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction.’ (3 September 1992, Vol. 1974 UN Treaty Series 2001, p. 45). Back
61 It is the most representative organ of the Organization for the Prohibition of Chemical Weapons, composed of all Members of the Organization (Article VIII (9)). Back
62 G. den Dekker, ‘Article XII: Measures to Redress a Situation and to Ensure Compliance, Including Sanctions’ in W. Krutzsch, E. Myjer & R. Trapp (eds.), The Chemical Weapons Convention: A Commentary (Oxford, OUP, 2014), p. 373. Back
63 Id., p. 367. Back


Convention cannot constitute legal grounds for the unilateral use of force by one of the State Parties. The only way the Convention could be linked to forcible measures, in case of the use of chemical weapons, is by bringing the issue to the attention of the UNSC, which may decide upon collective forcible measures. In any case, States are not authorized to act unilaterally because of a breach of the Convention.

When it comes to the UNSC resolutions 64 on the use of chemical weapons in Syria, the first of them, Resolution 2118, concerning events from 21 August 2013, was adopted on 27 September 2013. It condemned the chemical weapons attack (§ 2), and urged Syria not to use such weapons, as well as called upon other States not to support the further development of chemical weapons by Syria. The Resolution also claimed that the “use of chemical weapons in the Syrian Arab Republic constitutes a threat to international peace and security” and underlined that “Member States are obligated under Article 25 of the Charter of the United Nations to accept and carry out the Council's decisions” (Preamble). Moreover, the UNSC also decided “in the event of non-compliance with this resolution, including unauthorized transfer of chemical weapons, or any use of chemical weapons by anyone in the Syrian Arab Republic, to impose measures under Chapter VII of the United Nations Charter” (§ 21).

The same formula was subsequently reiterated in the UNSC Resolution 2209 (2015). 65 Then, on 7 August 2015 the UNSC established, by Resolution 2235, the Joint Investigative Mechanism of the United Nations and the OPCW to investigate cases of the use of chemical weapons in Syria. Again, the Resolution affirmed that the decision was “in response to violations of Resolution 2118 to impose measures under Chapter VII of the United Nations Charter” (§ 15). The mandate of the Mechanism was renewed by the UNSC Resolutions 2314 of 31 October 2016 and 2319 of 17 November 2016. No resolution was adopted after the chemical attack against civilians in Syria on 4 April 2017.

None of the resolutions mentioned above established sanctions against the Syrian regime because of its use of chemical weapons. The latest attempt to impose sanctions occurred on 28 February 2017, when over 40 States supported a draft resolution submitted to the UNSC, 66 a resolution which concerned, inter alia, freezing funds and banning the support or supply of individuals, enterprises and organizations within Syria linked to the chemical weapons industry, as enumerated in the Annex 1 to the Resolution. It also established an embargo on helicopters and a ban on the export of certain chemical precursors and dual-use items. Nevertheless, the Resolution was vetoed by China and Russia (Russia called it pointless since the “political processes in Astana and Geneva were working very well”). 67

Thus, despite the fact that the UNSC resolutions on Syria referred to Chapter VII of the UN Charter and to the possibility of implementing the measures included in that Chapter, it did not authorize any forcible measures, neither to be undertaken by the UNSC nor by any of the Member States. While it had previously happened that the UNSC allowed Member States “to take all necessary measures” - for instance to protect civilians (like in the broadly discussed UNSC Resolution 1973 of 11 March 2011, which was considered as the grounds for the launch of the military operation in Libya 68 ) - this was not the case in the resolutions referring to Syria. Thus, even the breach of, or noncompliance with, these

64 With regard to the use of chemical weapons in Syria, the UNGA adopted only one resolution, that is Resolution 68/182 of 18 December 2013, which condemned “the large-scale use of chemical weapons on 21 August 2013 in the Ghouta area of Damascus”. In addition, Resolution 71/130 of 16 December 2016 condemned the use of chemical weapons but without the reference to any particular attack (“Expressing outrage at the escalation of violence in the Syrian Arab Republic (…) including (…) the use of chemical weapons (…)”). Back
65 It recalls the UNSC Resolution 2118, and in this context decides that, in the event of further non-compliance with Resolution 2118, to impose measures under Chapter VII of the UN Charter (§ 7). Back
66 Albania, Australia, Austria, Belgium, Bulgaria, Canada, Croatia, Cyprus, Czechia, Denmark, Estonia, Finland, France, Germany, Greece, Iceland, Ireland, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Montenegro, Netherlands, New Zealand, Norway, Poland, Portugal, Qatar, Romania, Saudi Arabia, Slovakia, Spain, Sweden, Turkey, Ukraine, United Arab Emirates, United Kingdom of Great Britain and Northern Ireland and United States of America: draft resolution, S/2017/172. Back
67 UNSC Provisional Records, 72nd year, 7915th meeting, 5 April 2017, S/PV.7915, p. 16. Back
68 S. Bernstein, ‘The Responsibility to Protect After Libya: Humanitarian Prevention as Customary International Law’, Vol. 38 Brook Journal of International Law 2012-2013, pp. 305–306, 308. Back


resolutions could not constitute the grounds for the unilateral use of force by the United States against Syria.

II. States Reaction to the US Strike

On 7 April 2017, a UNSC meeting was convened in order to discuss the situation following the US strike against Syria.

Five States – the United Kingdom, France, Italy, Japan and Ukraine – explicitly supported the United States. The United Kingdom stressed that it endorsed the strike, since “war crimes have consequences” and “The United States strike was a proportionate response to unspeakable acts that gave rise to overwhelming humanitarian distress”. 69 The representative of Italy referred to the statement made by the Italian Minister of Foreign Affairs, who claimed that Italy understood the reasons for the US strike and considered it as “proportionate in time and manner and a response to a prolonged sense of impunity that is completely unacceptable”. According to Italy, it could also serve as a deterrent against further chemical attacks. 70 The French representative stated that France called for a strong reaction to the events in Syria, and in that context, the “American airstrike constitutes a legitimate response to the chemical attack”, adding that it had become “imperative to respond and deter the regime from such action”. 71 Japan declared that it supported the “determination of the United States Government to never allow the spread or use of chemical weapons” and that it understood “that the United States took the action last night in order to prevent further aggravation of the situation”. 72 Ukraine observed that the US strike was carried out to prevent “the regime from committing any further war crimes, including against the civilian population”, and added that it was “an appropriate and proportionate response”. 73 It should also be noted that the UN Under-Secretary-General for Political Affairs, in reporting on the US strike in Syria, mentioned that it is the UNSC which is primarily responsible for international peace and security, but in his statement there was not a note of criticism towards the US, but rather a reminder that the Council needs to give a “collective message” that the use of chemical weapons is prohibited, as well as that the international community should act together to protect civilians in Syria. 74 Outside the UNSC, the strike was unequivocally supported by Turkey, Saudi Arabia, Germany, Israel, Japan, Australia, Poland, Canada, as well as NATO and the European Union. 75

On the other hand, only two States which participated in the debate in the UNSC – Russia and Bolivia – expressed condemnation of the strike. The Russian ambassador spoke about an “attack on the territory of sovereign Syria”, a “flagrant violation of international law and an act of aggression”, as well as a violation of the 2015 memorandum on preventing air incidents and ensuring security during operations in Syrian airspace. 76 The representative of Bolivia observed that while the UNSC was discussing the use of chemical weapons against civilians and peaceful countermeasures to prevent the further use of such weapons, the US was preparing for the strike. As he stated: “Those missile attacks are indeed a unilateral action and represent a serious threat to international peace and security”. He also noted that the UN system was built to prevent the unilateral actions of powerful States against the weaker ones. Thus, he underlined that the UN Charter forbids unilateral actions and the use of force must be authorized by the UNSC. The Bolivian Ambassador also pointed out that a quite similar situation took place in 2003, when the US tried to convince the UNSC that Iraq possessed weapons of mass destruction, and subsequently started an intervention against Iraq; if that invasion had not taken place, today the world would not be

69 S/PV/7919, supra note 8, p. 5. Back
70 Id. , p. 8. Back
71 Id. , p. 9. Back
72 Id. , p. 10. Back
73 Id. , p. 16. Back
74 Id. , pp. 2–3. Back
75 ‘Syria war: World reaction to US missile attack’, 7 April 2017, Back
76 Id. , p. 10. Back


faced with the problem of the Islamic State. 77 Outside the UNSC, the strike was also condemned by Iran. 78

Most interestingly however, a number of States, such as China, Senegal, Ethiopia, Kazakhstan and Egypt, did not take a decisive position on the strike, 79 referring instead to peaceful means of resolution of disputes, as well as the need to prohibit the use of chemical weapons, without mentioning the US strike.

An interesting remark was offered by the representative of Uruguay, who underlined that his State rejected the legality of the unilateral use of force. However, Uruguay did not condemn the US’s actions, but declared that “Uruguay hopes that this individual incident, which occurred against the backdrop of the inability of the main Powers to resolve the conflict in Syria, does not lead to additional attacks (…)”. 80 Also, the Swedish Ambassador neither condoned nor condemned the US, but observed that every action needs to have grounds in international law, and that “[l]ast night’s missile attack also raises questions as to its compatibility with international law”. 81

It stems from the above that the majority of States did not condemn the US strike on the military base in Syria, even though none of these States pointed out any firm legal grounds for the operation. States which supported the US reiterated the US arguments about the humanitarian distress, the need for a ban on the use of the chemical weapons, and deterrence. However, in addition to American claims, they also mentioned proportionality, not as a criterion for the assessment of the legality of the self-defence, but as an independent basis for the action. Clearly some States (especially those five whose statements were the vaguest) had doubts about the legality of the strike, but at the same time they felt that condemning the US for the use of force, conducted in the aftermath of the deadly chemical attack against civilians, was not appropriate either. Thus, their position may be best summarized by the statements made by the representatives of Uruguay and Sweden: any case of the use of force needs to have grounds in public international law, but because of the reasons behind it, the American operation can hardly be condemned. Still the question arises: Did the American strike mark the start a new precedent for the use of force?

III. The Law on the Use of Force after 1945 82

Countless works have been prepared on the law of the use of force after 1945, and to review this scholarship would require a thick dissertation. 83 Hence the purpose of this article is not to review academic discussions, but to offer a brief summary of States’ practice and opinio juris in terms of the

77 Id., pp. 3–4. Back
78 Reuters, ‘Iran's Rouhani Warns Against More US Airstrikes on Syria, Says Attack 'Benefited Terrorism'’, 11 April 2017, Back
79 S/PV.7919, supra note 8, pp. 6–7, 9–10, 13–15. Back
80 Id., pp. 7–8. Back
81 Id., p. 14. Back
82 The author has prepared the PhD thesis on the unilateral use of force by States under customary international law and defended it in January 2018. Thus, the problems presented in this subchapter have been examined by the author in her thesis. Back
83 Much of this scholarship has been referenced in this article, e.g.: Brownlie, supra note 44; Bull, supra note 39; Cassese, supra note 5; Dinstein, supra note 9; Franck, supra note 55; Henkin, supra note 44; R. B. Lillich, supra note 39; Randelzhofer, supra note 4; Wilmshurst, supra note 46; Žourek, supra note 44; Ruys, supra note 4. Apart from that, one may enumerate, for example: T. Gazzini, The Changing Rules on the Use of Force in International Law (Manchester, Manchester University Press, 2005); C. Gray C., International Law and the Use of Force (Oxford, OUP, 2000); O. Corten, The Law against War: The Prohibition on the Use of Force in Contemporary International Law (Oxford and Portland, OR, Hart Publishing, 2012); M. J. Glennon, ‘The Rise and Fall of the U.N. Charter’s Use of Force Rules’, Vol. 27 No. 3 Hastings International and Comparative Law Review 2004; W. M. Reisman, ‘Criteria for the Lawful Use of Force in International Law’, Vol. 10 Yale Journal of International Law 1984-1985; B. Simma, ‘NATO, the UN and the Use of Force: Legal Aspects’, Vol. 10 European Journal of International Law 1999; A. J. Thomas, Jr. & A. van Wynen Thomas, Non-Intervention. The Law and Its Import in the Americas (Dallas, Methodist University Press, 1956); and M. Walzer, Just and Unjust Wars. A Moral Argument with Historical Illustrations (New York, Basic Books, 2000). Back


use of force after 1945, in order to highlight how the use of force in Syria in April 2017 differs from other similar cases of interventions.

It has been shown and is well known that the prohibition of the use of force included in Article 2(4) of the UN Charter has only one exception under the UN Charter which allows for the unilateral use of force, and that is the right to self-defence. However, before the UN Charter was adopted, States used force for many other reasons, not only to defend themselves, but also because of humanitarian needs, to rescue its nationals abroad who found themselves in danger, or simply to engage in conquest and expand their territories. The first formal limitation of the use of forcible measures was included in the II Hague Convention Respecting the Limitation of the Employment of Force for the Recovery of Contract Debts, 84 which forbade the use of force under very specific circumstances and envisaged exceptions to this ban. Nevertheless, it was only in 1928 that the Treaty between the United States and other powers providing for the renunciation of war as an instrument of national policy (also called the “Briand-Kellogg Pact”) was adopted, introducing the first absolute prohibition of the right to wage wars (with exception of self-defence, as its authors and State-Parties assumed). 85 Despite the many substantial flaws of the Briand-Kellogg Pact, 63 States became parties to the Pact, which meant that before World War II only four States were not bound by this treaty. 86 Due to its nearly universal character, it was claimed that the prohibition of war as an instrument of national policy was also a norm of CIL. 87

This short introduction to the state of law on the use of force before 1945 is necessary to highlight the changes that were introduced by the UN Charter, which undoubtedly can be called revolutionary. Article 2(4) of the Charter, forbidding the use of force “against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations”, along with Article 51 of the Charter, which sets out the strict criteria of lawful self-defence, are not only far more precise than all the previous regulations, but also make a clear statement about the lawful and unlawful conduct of States. However, does this mean States no longer deem such grounds for the use of force as “humanitarian intervention” or an “intervention to rescue nationals abroad” as lawful?

After 1945, there have been numerous cases of the unilateral use of force by States. 88 Despite that, those States which used force have always claimed the legality of their actions, searching in international law for legal grounds for their interventions and attempting to prove that they did not breach the prohibition of the use of force.

Basically, the cases on the use of force after 1945 may be divided into two groups: those justified by the intervening States based on the right to self-defence; and those which were justified on other legal grounds. When it comes to the use of force based on the right to self-defence, two further comments should be made. First, the interventions included in this group varied considerably, what shows is that States have interpreted right to self-defence in very different ways. The most substantial difference concerns the interpretation of the notion of an “armed attack”. States have claimed that an armed attack occurred in a series of cases of border clashes (the Israeli intervention in Egypt in 1956, the intervention of India in Pakistan in 1971, 89 the Vietnamese intervention in Cambodia in 1979, 90 and the claims of

84 J. B. Scott (ed.), The Hague Conventions and Declarations of 1899 and 1907 (New York, OUP, 3rd ed, 1918), p. 89. Back
85 Brownlie, supra note 44, p. 235; ‘Multilateral Treaty for Renunciation of War, Identical Notes of the Government of the United States to the Governments of Australia, Belgium, Canada, Czechoslovakia, France, Germany, Great Britain, India, The Irish Free State, Italy, Japan, New Zealand, Poland, South Africa’, Vol. 22 No. 3 The American Journal of International Law 1928, pp. 109–110. Back
86 I. Brownlie, Principles of Public International Law (Oxford, OUP, 6th ed, 2003), p. 698. Back
87 Trial of the Major War Criminals before the International Military Tribunal, Nuremberg 14 November 1045 – 1 October 1946, Vol. 1 (Nuremberg 1946), pp. 216–222. Back
88 There are no “official” statistics in this regard. In 2004, M. J. Glennon pointed out that since 1945 there were around 200 cases of the violation of the prohibition of the use of force (M. J. Glennon, ‘The Rise and Fall of the U.N. Charter’s Use of Force Rules’, Vol. 27 No. 3 Hastings International and Comparative Law Review 2004, p. 507), without differentiating between unilateral and collective interventions. The present author has examined over 30 cases of the unilateral use of force after 1945 in her PhD thesis. Back
89 UNSC Official Records, 11th year, 749th meeting, 30 October 1956, S/PV.749, §§ 33–36. Such claims were named in the doctrine of international law as the “accumulation of events” theory (Gazzini, supra note 53, pp. 143–144). Back
90 UNSC Official Records, 34th year, 2111th meeting, 15 January 1979, S/PV.2111, § 169. Back


Zambia of a right to self-defence against Portugal in 1969); 91 sabotage and infiltration (the US intervention in Lebanon 1958, the USSR in Afghanistan in 1979); 92 the arrest of a merchant vessel and its crew (the case of the US vessel S.S. Mayaguez); 93 a series of terrorist attacks (the US intervention in Libya in 1986); 94 plans to assassinate a former President (the US intervention in Iraq in 1993); 95 attacks against a State’s nationals living abroad (Russia in Georgia in 2003); 96 as well as a threat to the security of nationals abroad (the United Kingdom in Egypt in 1956, 97 Israel in Uganda in 1976 98 and the US in Panama in 1989). 99 It should also be observed that one of the States, namely Israel, has used force before an armed attack occurred on three occasions (in 1967, claiming that the United Arab Republic was planning an attack against it, 100 and twice when it suspected the construction of a nuclear reactor that could produce a nuclear weapon). 101

Secondly, usually States have invoked more than one justification for their use of force. Thus, apart from the self-defence as the main grounds for an intervention, States have referred to reasons which may be considered as either additional or alternative legal bases for the intervention. To give just an example, when the United States intervened in Lebanon in 1958, both the Lebanese and American authorities claimed that Lebanon had requested the US assistance on the grounds of the right to self-defence; 102 however, regardless of this justification US President Eisenhower claimed that the US government had to provide rescue for American citizens living in Lebanon since their life was endangered. 103 This was also true in the case of India, discussed above, when India claimed that its intervention in Pakistan was justified by self-defence, because of the “refugee aggression” and border clashes, in addition to the tragic humanitarian situation in East Pakistan. The United States claimed that the reason for its intervention in Libya in 1986 was both the breach of Article 2(4) by a series of terrorist attacks, as well as a pre-emptive action to deter further attacks. 104 When it intervened in Panama, the US claimed, apart from the right to self-defence, that there was a need to restore democracy, as well as pointed out Article IV of the Panama Canal Treaty, and the consent of the legitimate government of Panama. 105

When it comes to the cases of the unilateral use of force justified differently than by the right to self-defence, States have claimed that their actions were justified by a resolution of an international

91 UNSC Official Records, 24th year, 1486th meeting, 18 July 1969, S/PV.1486, §§ 6–11, 52, 57. Back
92 UNSC Official Records, 35th year, 2185th meeting, 5 January 1980, S/PV.2185, § 11, 14–17. Back
93 Letter Dated 14 May 1975 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security Council, S/11689. Back
94 UNSC Provisional Records, 2673rd meeting, 14 April 1986, S/PV.2673, pp. 12–15. Back
95 Letter dated 26 June 1993 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security CounciL, S/26003. Back
96 Letter dated 11 August 2008 from the Permanent Representative of the Russian Federation to the United Nations addressed to the President of the Security Council, S/2008/545. Back
97 The Secretary of State for Foreign Affairs, Middle East (Situation), HC Deb 31 October 1956 vol. 558, c 1565-1566. Back
98 UNSC Official Records, 31st year, 1939th meeting, 9 July 1976, S/PV. 1939, §§ 98, 104, 115, 119. Back
99 Letter Dated 20 December 1989 from the Permanent Representative of the United States of America to the United Nations Addressed to the President of the Security Council, S/21035. Back
100 UNSC Official Records, 22nd year, 1348th meeting, 6 June 1967, S/PV.1348, § 155. Back
101 Israel conducted an airstrike against the reactor built in Tammuz (Iraq) in 1981 (UNSC Provisional Records, 36th, 2280th meeting, 12 June 1981, S/PV.2280, § 58, 99–100), and in Al-Kibar (Syria) in 2007 (however, Israel never commented neither the attack, nor its legal basis). Back
102 UNSC Official Records, 13th year, 823rd meeting, 6 July 1958, S/PV.823, §§ 9–10, 15, 19; ‘Message to the Congress’, Vol. XXXIX No. 993 The Department of State Bulletin 7 July 1958, p. 182; and ‘Statement by President Eisenhower, White House press release dated July 15’, Vol. XXXIX No. 993 The Department of State Bulletin 7 July 1958, p. 181. Back
103 UNSC Official Records, 13th year, 831st meeting, 17 July 1958, S/PV.831, §§ 18–26. Back
104 ‘U.S. Exercises Right of Self-Defense Against Libyan Terrorism. President’s Address to the Nation, April 14, 1986’, Vol. 86 No. 2111 Department of State Bulletin June 1986, p. 1. Back
105 ‘Fighting in Panama: The State Dept.; Excerpts From the Statement by Baker on U.S. Policy’, 21 December 1989,; L. Henkin, ‘The Invasion of Panama Under International Law: A Gross Violation’, Vol. 29 Columbia Journal of Transnational 1991, p. 297, 299; A. Tancredi ‘The Russian Annexation of the Crimea: Questions Relating to the Use of Force’, Vol. I Questions of International Law, Zoom Out 2014, p. 16. Back


organization (the “defensive quarantine” applied by the US against Cuba in 1962 106 ), treaty provisions (Turkish intervention in Cyprus in 1964), 107 the consent on the part of a regional organization (the US intervention in the Dominican Republic in 1963), 108 the need to rescue hostages abroad together with the consent of the local government (Belgium in Congo in 1964), 109 the request of the alleged State authorities (USSR in Hungary in 1956) 110 or a request by the local people (Indonesia in East Timor in 1975). 111 Once again it frequently happened that States invoked several justifications, especially if they could hardly find any legal or factual grounds explaining the reasons behind their intervention. For example, following its intervention in Ukraine in 2014, Russia claimed that it had to intervene because of the persecution of the Russian-speaking minority in Crimea 112 and on the basis of a request for intervention from the Crimean authorities. Although, most interestingly Russia argued that the intervention in Crimea did not breach Article 2(4) of the UN Charter at all, since Russia did not carry any armed activities in Crimea and President Putin asked the Federation Council about the deployment of forces “on the territory” of Ukraine and not “against Ukraine”. 113

These numerous examples make it possible to draw some general conclusions. First of all, the most frequently offered justifications for the unilateral armed interventions were self-defence, consent for the intervention, a treaty basis and the authorization of an international organization. If States challenged the legality of these interventions, they questioned the circumstances connected with its factual background (e.g. consent obtained from unlawful authorities, pressure put on an international organization to gain authorization, etc.), but they did not challenge the assertion that these legal bases could constitute a justification of the use of force. Thus, one may claim that, apart from the self-defence, there are a few legal bases that are acknowledged as allowing States to use force unilaterally.

Secondly, no matter how much the factual circumstances of interventions may have been insufficient to make them truly lawful, States have endeavoured to find legal justifications for these interventions and prove that they did not breach the prohibition of the use of force. Thus, paradoxically, all these cases of interventions in fact reinforce the validity of the prohibition of the use of force, since none of the States have claimed after 1945 that they were not bound by the prohibition of the use of force contained in the UN Charter. 114

Thirdly, there are hardly any examples after 1945 when the intervening States failed to make explicit claims about the legal grounds of their interventions; 115 the present author is aware of two such interventions – the intervention of Tanzania in Uganda in 1979, and the Israeli strike against the Al-Kibar reactor. Tanzania claimed that it responded to the Ugandan intervention, without recalling self-defence,

106 A. Chayes, ‘Law and the Quarantine of Cuba’, Vol. 41 Foreign Affaires 1962-1963, p. 555. Back
107 UNSC Official Records, 19th year, 1142nd meeting, 8 August 1964, S/PV.1142, §§ 57–59, 67. Back
108 Kanakaratne, supra note 27, pp. 107–108. Back
109 S/6063, supra note 34, p. 3; Weisberg, supra note 34, p. 263; Letter Dated 24 November 1964 from the Prime Minister of the Democratic Republic of Congo Addressed to the Secretary-General, S/6060. Back
110 Higgins, supra note 45, p. 210; Schmeltzer, supra note 28, p. 112. Back
111 UNGA Official Records, 30th session, 2185th meeting, Fourth Committee, 8 December 1975, A/C.4/SR.2185, § 32; UNSC Official Records, 30th year, 1864th meeting, 15 December 1975, S/PV.1864, §§ 88, 92–93. Back
112 ‘Speech of the President of the Russian Federation’, 18 March 2014, Back
113 UNSC Provisional Records, 69th year, 7124th meeting, 1 March 2014, S/PV.7124, pp. 2, 5. Back
114 Similarly, see Henderson, supra note 47, p. 7; Cassese, supra note 44, p. 514. This standpoint was also supported by the ICJ in the Nicaragua case: “It is not to be expected that in the practice of States the application of the rules in question should have been perfect, in the sense that States should have refrained, with complete consistency, from the use of force or from intervention in each other's internal affairs. (…) the Court deems it sufficient that the conduct of States should, in general, be consistent with such rules, and that instances of State conduct inconsistent with a given rule should generally have been treated as breaches of that rule, not as indications of the recognition of a new rule. If a State acts in a way prima facie incompatible with a recognized rule, but defends its conduct by appealing to exceptions or justifications contained within the rule itself, then whether or not the State's conduct is in fact justifiable on that basis, the significance of that attitude is to confirm rather than to weaken the rule.” (ICJ, Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), 27 June 1986, I.C.J. Rep 1986, p. 14, § 186) Back
115 Present author is aware of the such incidents as the strikes against non-state actors, cyberattacks etc. However, “hardly any” should be read in the context of this article, which refers only to unilateral interventions, conducted with the direct use of armed force by armed forces of a State against another States. Back


and declared that the intervention constituted a retaliation against Uganda. 116 While Israel on the other made a general comment on the strike very recently, after over a decade, factual grounds for the attack may be interpolated only from the US intelligence information, 117 which indicated that the reactor in Al-Kibar could have served not only as electricity plant but also as nuclear weapons factory, which could potentially be used against Israel. Moreover, in both these cases the reaction on the part of the international community was very sparse and restrained. As regards the intervention of Tanzania, right before the Tanzanian troops were about to reach Kampala, Ugandan president Idi Amin twice requested UN assistance, but requests were left unheard. 118 The only two States which openly criticized the Tanzanian intervention were Nigeria and Sudan; the rest of the international community recognized the new Ugandan government established in the aftermath of the intervention within a short time. 119 T. M. Franck argues that States were reluctant to support Amin, who had committed crimes against Uganda’s own nationals, 120 but despite the recognition of the new Ugandan government, States were also reluctant to openly support the Tanzanian intervention or refer to its potential legal justification. 121 In the case of Israel, the only State that openly criticized the strike was North Korea; the US and Canada mentioned the Al-Kibar reactor and condemned North Korea for the support it had given to the Syrian authorities in the construction of the reactor, but did not mention the Israeli attack at all. 122

The above conclusions should be borne in mind when analysing the unilateral use of force conducted by the United States against Syria via its strike in April 2017. When it comes to the four legal grounds of support for unilateral cases of the use of force mentioned above, the use of chemical weapons against civilians, as well as the need to “prevent and deter” a potential threat to the United States and its allies cannot be deemed to have constituted sufficient legal grounds for the launch of the military action. Undoubtedly the reasons behind the US strike are understandable in terms of their morality and pragmatism, however, politics and pragmatism were also rationales behind some of the interventions conducted before 1945, while their deadly results and the instability they caused were the reasons for the introduction of the prohibition of the use of force in the UN Charter.

On the other hand, the third argument invoked by President Trump – the breach of the Chemical Weapons Convention and the UNSC resolutions on Syria – could be deemed to be an attempt to refer to one of the legal grounds for the unilateral use of force discussed above, i.e. a treaty norm and authorization on the part of an international organization. However, one needs to observe that in cases of the use of force when such legal grounds have been invoked, either there was a treaty norm that could allow for the military intervention, at least by applying its broad interpretation, or the UNSC resolution allowed States to “take all necessary measures”, which is usually interpreted as an authorization for the use of force. In contrast, neither the Chemical Weapons Convention, nor any of the UNSC resolutions on Syria authorized the unilateral use of force against Syria for its use of chemical weapons against civilians, even if they are interpreted very broadly.

To sum up, the justification for the intervention, as given by President Trump and the US representatives, does not fit into the high standards required to justify the unilateral use of force by States, as established after 1945.

At the same time, as has been described above, it has happened (albeit rarely) that States have used force unilaterally without giving a sufficient explanation, or even justifying their conduct at all. In this context,

116 N. J. Wheeler, Saving Strangers: Humanitarian Intervention in International Society (Oxford, OUP, 2000), pp. 120–121. Back
117 As reported by media, Israeli prime minister stated that the attack was conducted in order “to prevent our enemies from arming themselves with nuclear weapons” (BBC News, ‘Israel admits striking suspected Syrian nuclear reactor in 2007’, 21 March 2018,; and ‘Background Briefing with Senior U.S. Officials on Syria’s Covert Nuclear Reactor and North Korea’s Involvement’, 24 April 2008,, pp. 1–3, 4, 8, 11–12. Back
118 Letter dated 28 March 1979 from the Deputy Permanent Representative of Uganda to the United Nations Addressed to the President of the Security Council, S/13204; Wheeler, supra note 100, pp. 122–123. Back
119 Wheeler, supra note 116, pp. 123–128; Akehurst, supra note 39, pp. 98–99. Back
120 Franck, supra note 55, pp. 144–145. Back
121 Wheeler, supra note 116, pp. 123–124. Back
122 L. S. Spector, A. Cohen, ‘Israel’s Airstrike on Syria’s Reactor: Implications for the Nonproliferation Regime’, Back

the US intervention in Syria is not a new occurrence. However, there are some differences between the April strike and the interventions discussed above. First and foremost, the United States conducted an attack against a State that did not constitute a direct threat to the United States. It is very unlikely that if the strike had not taken place the Syrian authorities could potentially have used the attacked military base for attacks against the United States, or even the US allies. These doubts are reinforced by the statements made by President Trump – he mentioned the chemical weapons attack against Syrian nationals (without mentioning any threat to American citizens), the proliferation of chemical weapons (without claiming that there was any particular threat to the United States connected with Syria’s possession of chemical weapons), as well as the refugee crisis (which hardly affects the United States at all). Even if the US understands its “security interests” very broadly, including not only the direct threats against the US, but also against “its allies”, this does not change the fact that the United States put itself into the position of “global policeman”, and regardless of whether there was or was not any direct danger, decided to react just because a wrong was taking place. Thus, in contrast to the interventions mentioned above, especially including the intervention of Tanzania in Uganda and the Israeli airstrike against Al-Kibar, the United States not only failed to give any legal grounds for its strike, but also conducted it in the absence of any direct threat for the US or “its allies”. Thus, it should be reiterated that such conduct on the part of States in the past was the reason for the introduction of the prohibition of the use of force, as well as initiating the collective security system.

While it is true that the UNSC was paralyzed by the Russian and Chinese approaches and could not, in the current political realities, agree upon any collective forcible measures against Syria, one could question whether the United States had exhausted all measures within the collective security system in order to justify the claim that the collective security system turned out to be insufficient. In this regard, it is noteworthy that none of the draft resolutions voted upon at the UNSC meeting proposed allowing for forcible measures against Syria (without prejudice to the fact that Russia and China would have vetoed them anyhow), 123 and more importantly, the United States did not seek any other options. In this latter regard one may mention the UNGA Resolution 377 (V) “Uniting for Peace”, which is meant to allow the UNGA to decide about measures necessary “to maintain or restore international peace and security” when the UNSC fails to exercise its functions due to the requirement of “unanimity of the permanent members” (§ 1). 124 There is no information that the United States sought any such support.

However, as long as the United States violated international law by the strike, it is much more important how this act influenced, or may influence, the shape of jus ad bellum rules, especially given the reaction of other States to the strike. The examination of this issue requires both the analysis of CIL, and the interpretation of the UN Charter. To start with CIL, one needs to make a few remarks on the formation of CIL. The majority of authors nowadays support the view that there are two constitutive elements of customary norms, namely practice (usus) and acceptance of the practice as law (opinio juris); 125

123 A very good account of all the failed UNSC resolutions on Syria is presented in a post by E. McKirdy, ‘8 times Russia blocked a UN Security Council resolution on Syria’, 13 April 2017, Back
124 UNGA Res. 377 (V), 3 November 1950. Back
125 G. J. Postema, ‘Custom in international law: a normative practice account’ in A. Perreau – Saussine & J. B. Murphy (eds.), The nature of customary law: Legal, historical and philosophical perspectives (Cambridge, CUP, 2007), p. 280; H. Thirlway, The Sources of International Law (Oxford, OUP, 2014), pp. 56–57; Cassese, supra note 4, p. 158; J. Crawford, Brownlie’s Principles of Public International Law (Oxford, OUP, 2012, 8th ed.), p. 23; L. Kopelmanas, ‘Custom as a Means of the Creation of International Law’, Vol. 18 British Year Book of International Law 1937, p. 135; S. Oeter, ‘The Legitimacy of Customary International Law’, in T. Eger, S. Oeter & S. Voigt (eds.), Economic Analysis of International Law. Contributions to the XIIIth Travemünde Symposium on the Economic Analysis of Law (March 29-31, 2012) (Tübingen, Mohr Siebrek, 2014), p. 16; and H. Taki, ‘Opinio Juris and the Formation of Customary International Law: A Theoretical Analysis’, Vol. 51 German Yearbook of International Law 2008, p. 466. However, one needs to underline that there are authors who claim that only one of these elements contribute to the formation of customary norms, either practice (see e.g. findings of the International Law Association, ‘Committee on Formation of Customary (general) International Law: Final Report of the Committee’, p. 9, or opinio juris (R. B. Baker, ‘Customary International Law in the 21st Century: Old Challenges and New Debates’, Vol. 21 No. 1 The European Journal of International Law 2010, p. 182; A. T. Guzman, ‘Saving Customary International Law’, Vol. 27 Michigan Journal of International Law 2005, p. 122; and B. D. Lepard, Customary International Law: A New Theory with Practical Applications (Oxford, OUP, 2010), pp. 97–98). Nevertheless, this article adopts the two elements definition of customary norm. Back


moreover, this standpoint is also adopted by States 126 and in the international case law. 127 The two elements definition is also the foundation of the definition of custom from Article 38 (1) (b) of the ICJ Statute. There are neither conclusive lists of acts of States which qualify as practice or opinio juris, nor clear criteria which would enable to distinguish between these two elements. This article adopts the view that practice may take the form of physical and verbal acts, 128 while opinio juris includes, inter alia, “public statements made on behalf of States”. 129 Given that, both the US strike, and the reaction of States to this act, are relevant for the process of formation of CIL.

As it was claimed above, the prohibition of the use of force is a contemporary customary norm. It was also depicted that that even if States violated the prohibition after 1945, the justifications they provided for the armed interventions, all along with the reaction of other States, which condemned these interventions, in fact reinforced the validity of the prohibition. Thus, not every violation of customary norm prompts its change or termination. In that case, when does a violation of customary norm prompt the modification of a norm? On one hand, one may repeat the example given by J. P. Trachtman: if ten States accept that there is a customary norm imposing the carbon reduction, and one State violates this rule, the further existence of the rule will depend on the reaction of the remaining nine States: if they continue to comply with the existing norm, the tenth State violates international law; however, if the other States decide to follow this tenth State and violate the rule, the existing rule may become revised. 130 However, “no practice, however abundant, can of itself change a customary rule as long as it is not accepted as constituting such a change”. 131 Thus, to modify the existing customary norm, the change of attitude of one State is not sufficient; other States need to follow this attitude, however, not as a violation of a norm but as a desired change of this norm.

Bearing that in mind, one may assess the relevance of the US strike and the reaction of other States for the formation of CIL. When it comes to the US, the strike undoubtedly may be qualified as practice. However, is it relevant for the process of formation of CIL that the US did not refer to the legal grounds of the strike? Since the US provided some argumentation, even though not legal one, one may come to the conclusion that the US considered political and moral reasons as sufficient to use force and found it unnecessary to invoke in-depth legal justification. Nevertheless, even so, this singular example cannot influence the formation of CIL and change the shape of norms regulating the use of force. However, if in future it happens again and again States, violating the prohibition of the use of force, do not refer any legal justifications but limit themselves to arguments connected with fairness, humanitarianism, etc. it may signify that in fact States accept the use of force for extra-legal reasons as permissible, which, prospectively, could influence the formation of CIL.

When it comes to States’ reaction for the strike, States that clearly supported the US, reiterated the US argumentation rather than sought legal grounds of the US action. Thus, the fact that they accepted the US position, did not look for the grounds of the US action under international law and referred itself to moral reasoning, means that in fact they accepted that the US could use force, even though there were no legal grounds for that, and, what’s more, in such case no legal justification was needed. However, as mentioned above, some States did not take a decisive position on the strike. These States were clearly concerned by the compliance by the US with international law, but in the meantime they did not feel

126 International Law Commission, ‘Second report on identification of customary international law, by Sir Michael Wood, Special Rapporteur’, A/CN.4/672, § 24. Back
127 ICJ, North Sea Continental Shelf (Federal Republic of Germany/Denmark), 20 February 1969, I.C.J. Rep 1969, p. 3, § 77; Military and Paramilitary Activities in and against Nicaragua, supra note 114, § 207. Back
128 International Law Commission, ‘Text of the Draft Conclusions Provisionally Adopted by the Drafting Committee’, A/CN.4/L.872, Draft Conclusion 6[7] (1); R. van Steenberghe, ‘State Practice and the evolution of the law of self-defence: clarifying the methodological debate’, Vol. 2 No. 1 Journal of the Use of Force and International Law 2015, p. 85; Postema, supra note 125, p. 291 Back
129 A/CN.4/L.872, supra note 128, Draft conclusion 10 [11] (2). Back
130 J. P. Trachtman, ‘Persistent Objector, Cooperation, and the Utility of Customary International Law’, Vol. 21 Duke Journal of Comparative & International Law 2010-2011, p. 229. Back
131 K. Wolfke, Custom in present international law (Dordrecht, Springer, 1993), p. 65. Back


comfortable criticizing a strike against a government which committed crimes against its own citizens. Again, that is where the politics appears all along with international law. Thus, it is hard to assess whether they refrained from straightforward condoning or condemning the US strike because they did not want to be labelled as defenders of president Assad, they wanted to uphold the validity of the prohibition of the use of force, or because they really thought that the US did not invoke sufficient arguments for the strike. Again, the relevance of their attitude for international law cannot be evaluated using this singular example; it is indispensable to observe the approach they will adopt in the future. Finally, the group of States expressly condemned the US, using legal arguments.

However, above all, States which publicly commented on the US strike constitute only a small part of the international community. While it is true that while identifying the customary norms, one usually evaluates only practice and opinio juris of the most powerful States or those ones which are particularly interested in the given issue, while the attitude of the rest of States is omitted, and as well as silence may be qualified as acquiescence, 132 given that the problem concerns one of the most fundamental norms of international law, the position of around twenty States is definitely not enough to change the state of CIL.

Summing up, the US strike is not a precedent that modified the customary norm prohibiting the use of force. It was the first violation of the prohibition of the use of force of this kind, both when it comes to the lack of the US legal justification, and approval of such attitude adopted by some of the States. However, since this case constitutes such a departure from the previous approach to the prohibition of the use of force, one needs to observe whether States continue to follow this pattern in the future.

When it comes to the interpretation of the UN Charter, and most importantly, Article 2(4), it is quite obvious that if the practice and opinio juris are about to form a new customary norm on the use of force, grounded on such cases as the US strike, it would be contrary to Article 2(4). It is true that two norms, a customary norm and a treaty norm, governing the same area, may co-exist, and they do not have to be identical in content. 133 However, if they differ considerably, it leads to uncertainty as to the scope of binding obligations for States. 134 More so, if this problem concerns the UN Charter, so the legal act of nearly universal participation, and the universal customary norm, the chaos created by co-existence of two such norms could be particularly dangerous. It is also possible that the customary norm different from the treaty norm, which regulates the same area, may change the way the treaty norm is interpreted; 135 however, if the customary norm not only differs, but is simply conflicting with the treaty norm, the treaty could be modified by the application of this customary norm. 136 It means that, first and foremost, the customary norm allowing for the broad use of force would have to be formed, and secondly, States would have to stop validating the prohibition from Article 2(4). Both these options are highly improbable nowadays, given the strong support for the validity of Article 2(4) expressed from 1945 up to now. Given that the modification of the treaty may take place due to the “subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation”, 137 the remarks made above may be referred also to the problem of modification of the UN Charter through the “subsequent practice”, since it will not be easy to reach an agreement as to the interpretation of Article 2(4) allowing for the broad use of force. 138

132 Oeter, supra note 125, p. 15. Back
133 Nicaragua, supra note 114, § 175. Back
134 O. Schachter, ´Entangled Treaty and Custom’, in Y. Dinstein (ed.) International Law at a Time of Perplexity. Essays in Honour of Shabtai Rosenne (Dordrecht, Springer, 1989), p. 728. Back
135 A. D’Amato, ‘Trashing Customary International Law’, Vol. 81 No. 1 The American Journal of International Law 1987, p. 105. Back
136 Gazzini, supra note 53, p. 120. Back
137 Vienna Convention on the law of treaties (with annex), Vienna, 23 May 1969, Vol. 1155 No. 18232 UN Treaty Series 1980, Article 31 (3) (b). Back
138 See I. Buga, Modification of Treaties by Subsequent Practice (Oxford, OUP, 2018); S. D. Murphy, ‘The Relevance of Subsequent Agreement and Subsequent Practice for the Interpretation of Treaties’, in G. Nolte (ed.), Treaties and Subsequent Practice (Oxford, OUP, 2013). Back


Thus, these two circumstances – the discretion involved in the US actions and the lack of condemnation in that regard from a considerable group of States – could be possibly dangerous for the validity of the prohibition of the use of force, and could mark the beginning of the new trend in international law. Although for now, one cannot claim that the case of the US strike of April 2017 introduced any change to the state of international law when it comes to the absolute prohibition of the use of force, as expressed in Article 2(4) of the UN Charter and in customary norm.


Since 1945 States have on frequent occasions used force unilaterally, breaching the prohibition contained in Article 2(4) of the UN Charter. However, even in doing so almost all States have endeavoured to justify their actions by self-defence, an existing treaty norm, consent of the attacked state, or authorization of an international organization, no matter how far these justifications deviated from the factual background of the interventions carried out. Thus, paradoxically in the end these States, by their actions, confirmed their recognition of the validity of the prohibition of the use of force. In comparing these previous cases of the use of force to the US strike in Syria on 7 April 2017, the US strike may be seen as an especially flagrant breach of the prohibition of the use of force. President Trump not only did not mention international law at all when explaining the reasons behind the intervention, but also the reasons which he gave demonstrated that the intervention was unlawful. Thus, even though the US intervention is understandable in terms of its morality and political pragmatism, it nevertheless constitutes a serious breach of international law. However, despite the fact that the intervention was not condemned (or was even explicitly supported) by few States, it is hard to claim that it constituted the turning point in the evolution of the paradigm of the use of force since the standpoint of around twenty States is not enough to change the most fundamental norm of contemporary international law. Only attitudes adopted by States in the future will prove whether the US intervention initiated a more profound shift in the shape of the prohibition of the use of force. 139

139 This article was accepted for publication before the US, the United Kingdom and France conducted the strikes on 14 April 2018 and does not include the analysis of this case of use of force. Back