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The Use of Force in International Law - A Case-Based Approach edited by Ruys, Tom; Corten, Olivier; Hofer, Alexandra (17th May 2018)

Part 3 The Post 9/11-Era (2001–), 64 The Military Operations Against the ‘Islamic State’ (ISIL or Da’esh)—2014

Olivier Corten

From: The Use of Force in International Law: A Case-Based Approach

Edited By: Tom Ruys, Olivier Corten, Alexandra Hofer

Subject(s):
Terrorism — Necessity — Self-defence — Sovereignty — UN Charter — Military matters

(p. 873) 64  The Military Operations Against the ‘Islamic State’ (ISIL or Da’esh)—2014

I.  Facts and Context

The so-called ‘Islamic State’ is a terrorist group that proclaimed itself as a ‘world caliphate’ on 29 June 2014.2 Initially linked to ‘Al Qaeda in the Arabic Peninsula’ (AQAP), the Islamic State (IS) was previously known as the ‘Islamic State of Iraq’ (ISI, from 2006 to 2013), and later the ‘Islamic State of Iraq and the Levant’ or the ‘Islamic State of Iraq and Syria’ (ISIL or ISIS, from 2013). The acronyms IS, ISIL, ISIS, or ‘Da’esh’ (derived from Arabic) are used interchangeably, albeit UN official documents generally refer to ‘ISIL’.3

It is generally considered that ISIL was created by armed opponents to the Iraqi Government installed in the aftermath of the 2003 US-led intervention in Iraq.4 Originally, its members essentially opposed the Baghdad authorities, which were accused of providing Iraq’s Shia majority with disproportionate benefits and of oppressing the Sunni minority with the support of foreign powers. However, ISIL quickly expressed broader ambitions; from 2013 onwards, it claimed exclusive political and theological authority over the world’s Muslims and succeeded in attracting many fighters from foreign countries, mainly from the Arab World, western Europe, Russia (particularly Chechnya), and North Africa. Some sources also suggest that ISIL has been supported by—or from—other states like Saudi Arabia or Turkey, either financially or even through the provision of arms.5 Moreover, the gains made against the Iraqi army, facilitated by the massive withdrawal of US troops in 2011, enabled the organization to acquire a considerable amount of military equipment, as well as control of numerous oil facilities. Another important element was the development of the Syrian war, which led to a power vacuum in substantial parts of the Syrian territory that ISIL soon exploited. Those factors help explain why, in 2014, ISIL was able to control an impressive stretch of territory, crossing the Iraqi–Syria boundary—a boundary ISIL denounced as a product of the colonial division of the world.6 This self-proclaimed (p. 874) ‘Islamic State’ thus managed to control a vast amount of territory, in which it installed a de facto government, and elaborated a domestic political, legal, and judicial system based on a particularly radical interpretation and application of the sharia. Numerous sources have denounced massive violations of human rights in the ISIL controlled territories.7 ISIL has been labelled a terrorist organization by the UN as well as by numerous organizations and states.8 By contrast, and unsurprisingly, it has never been recognized as a ‘state’.9 Indeed, amongst other things, the effectiveness of the IS authorities is indeed unstable and fragile, and, above all, is undermined by serious violations of peremptory norms of international law, such as the right to life or the prohibition of torture.10

Against this background, and after having lost the strategic city of Mosul, in the north of the country, to ISIL, Iraq sent a letter to the Security Council on 25 June 2014, in which it stated that:

ISIL has … been terrorizing citizens, carrying out mass executions, persecuting minorities and women, and destroying mosques, shrines and churches. This group now threatens several governorates, including Baghdad, thanks to external support and the influx of thousands of foreign terrorists of various nationalities from across the border in Syria … The situation has become more serious over the past two years, as ISIL has repeatedly launched attacks against Iraqi territory from eastern Syria … We therefore call on the United Nations and the international community to recognize the serious threat our country and the international order are facing … To that end, we need your support in order to defeat ISIL and protect our territory and people. In particular, we call on Member States to assist us by providing military training, advanced technology and the weapons required to respond to the situation, with a view to denying terrorists staging areas and safe havens …11

A few weeks later, on 7 August 2014, President Obama announced the launching of a military action against ISIL. Airstrikes within Iraqi territory began in the following days, whereas arms and equipment were provided to the Kurdish combatants who fought ISIL in the north of the country. The United States were quickly joined by numerous other states, as was revealed in a second letter sent to the UN by the Iraqi authorities on 25 September:

On 15 September 2014, at the Paris conference, the international community attested to the fact that ISIL represents a threat to Iraq. We welcome the commitment that was made by 26 States to provide the new Iraqi Government with all necessary support in its war against ISIL, including appropriate military assistance through the provision of air cover in coordination (p. 875) with the Iraqi armed forces and in accordance with international law … Iraq is grateful for the military assistance it is receiving, including the assistance provided by the United States of America in response to Iraq’s specific requests …

As we noted in our earlier letter, ISIL has established a safe haven outside Iraq’s borders that is a direct threat to the security of our people and territory. By establishing this safe haven, ISIL has secured for itself the ability to train for, plan, finance and carry out terrorist operations across our borders. The presence of this safe haven has made our borders impossible to defend and exposed our citizens to the threat of terrorist attacks.

It is for these reasons that we, in accordance with international law and the relevant bilateral and multilateral agreements, and with due regard for complete national sovereignty and the Constitution, have requested the United States of America to lead international efforts to strike ISIL sites and military strongholds, with our express consent. The aim of such strikes is to end the constant threat to Iraq, protect Iraq’s citizens and, ultimately, arm Iraqi forces and enable them to regain control of Iraq’s borders.12

The Iraqi Government obtained considerable support, with France (‘Operation Chammal’),13 the Netherlands, Belgium, the United Kingdom (‘Operation Shader’),14 Australia, Denmark, Canada, Morocco, and other Arab states all participating in strikes against ISIL. For his part, UN Secretary-General Ban Ki-Moon called for ‘decisive action’,15 and many other countries soon joined the coalition, some of them participating in military actions, others supporting it by other means. In December 2014, the US Central Command announced the creation of a ‘Combined Joint Task Force’ to coordinate military actions as part of a unique multinational ‘Operation Inherent Resolve’.16 This coordination did not, however, prevent some states, such as Turkey, from launching military actions of their own, in certain cases without the support of the other intervening states.

On 23 September 2014, the United States, Bahrain, Jordan, Qatar, Saudi Arabia, and the United Arab Emirates began launching strikes against ISIL within Syrian territory.17 The western members of the coalition (other than the United States) were initially reluctant to follow that path and—at least initially—confined their operations to Iraqi territory. Indeed, the fact that the Syrian Government had never issued an official invitation to the US-led coalition, as its Iraqi counterpart had done, was perceived by some states as creating a legal obstacle.18 It can be observed in this context that the Damascus authorities had clearly expressed their readiness to consent to a foreign intervention on the Syrian territory to combat Da’esh. In August 2014, they stated that:

(p. 876)

Syria is ready to cooperate and coordinate with regional and international efforts to combat terror in accordance with UN resolutions and respect of Syrian sovereignty … Everyone is welcome, including Britain and the United States, to take action against ISIS and Nusra with a prior full coordination with the Syrian government.19

A few months later, whilst combats between the governmental and ISIL forces continued on the Syrian territory, the Syrian Government reiterated that it was ready ‘to cooperate bilaterally and at the regional and international levels to combat terrorism’20 and this was confirmed several times afterwards.21 On the other hand, many members of the US-led coalition did not want to support, even indirectly, the Assad regime by helping it defeat one of its enemies.22 Against this background, it must be noted that the Syrian Government did not officially complain23 of the strikes on its territory from September 2014 to September 2015 with the beginning of the Russian intervention. During this period, Syria seemed unsurprisingly satisfied by the massive military strikes against ISIL that allowed the governmental forces to redirect most military operations against other groups of rebels.24

Different factors led to a radical change of the nature of the conflict by the end of 2015. In particular, Russia decided to support the Assad regime by providing military assistance in ‘combating the terrorist group Islamic State in Iraq and the Levant (ISIL) and other terrorist groups operating in Syria’.25 ISIL was now confronted not only with a US-led coalition but also with a coalition between Syria, Russia, and—to a lesser extent—Iran, which moreover received additional support from the non-state ‘Hezbollah’ militia from neighbouring Lebanon. It is against this background that ISIL claimed responsibility for a large range of terrorist acts on the territory of states involved in the coalition, the most known having stricken France (13 November 2015), Belgium (22 March 2016), and Turkey (on various occasions). Those events in turn led those states to intervene more intensively against ISIL, and inspired a number of (western) members of the US-led coalition that had hitherto confined their operations to Iraqi territory to expand their operations to Syrian territory as well.

On 20 November 2015, the Security Council, which had so far adopted several resolutions or declarations strongly condemning ISIL as a terrorist organization, unanimously adopted Resolution 2249 (2015), in which it

[called] upon Member States that have the capacity to do so to take all necessary measures, in compliance with international law, in particular with the United Nations Charter, as well (p. 877) as international human rights, refugee and humanitarian law, on the territory under the control of ISIL also known as Da’esh, in Syria and Iraq, to redouble and coordinate their efforts to prevent and suppress terrorist acts committed specifically by ISIL also known as Da’esh as well as ANF, and all other individuals, groups, undertakings, and entities associated with Al Qaeda, and other terrorist groups … and to eradicate the safe haven they have established over significant parts of Iraq and Syria.26

Whatever the potential legal implications of this resolution are, it was clear that ISIL was confronted to a strong and resolved opposition by the UN and all of its member states. Despite the differences that characterized the political positions of different groups of states (mainly the US- and the Russian-led coalitions), all the foreign intervening states began to coordinate their military operations against ISIL to avoid incidents or casualties. It is therefore not surprising that, in 2016, a year in which the Russian involvement on the battlefield increased significantly, ISIL lost control of various cities and territorial gains it had made.27 At the same time, some extremist groups operating in Libya and Afghanistan—among other countries—pledged their allegiance to the caliphate, and suffered military attacks by the governments of those states, as well as by some of their allies.

At the time of writing, the outcome of the conflict remains uncertain. In the following parts, we address the legal aspects of the precedent by focusing on the military interventions by foreign states in Iraq and in Syria, leaving aside other aspects of the fight against ISIL like the civil war in Syria with rebel groups other than ISIL or the specific situations that developed in other states like Libya or Afghanistan. Other aspects of the Syrian conflict—for instance the Russian intervention against rebels not linked to ISIL, the dispute between Russia and Turkey concerning the downing of a Russian jet in November 2015, or the US strikes against the regime in April 2017—will not be addressed here.

II.  The Positions of the Main Protagonists and the Reaction of Third States and International Organizations

Many states and actors have expressed a position with regard to the military actions against ISIL, mainly in three different ways: first during the various debates that have taken place within the UN about the conflict, second by sending official letters to the UN, and third through more informal ways outside the UN. While it is simply impossible to provide an exhaustive description of the existing statements and declarations,28 the present section provides a general survey by distinguishing the two main arguments put forward to justify the military operations concerned, namely the consent of the Iraqi and Syrian Governments, on the one hand, and self-defence, on the other hand.29

(p. 878) 1.  The consent of the Iraqi and the Syrian Governments

As mentioned above, Iraq sent two letters to the UN requesting foreign support in the fight against ISIL. Those letters were, unsurprisingly, invoked as a legal basis supporting the ensuing interventions. On 23 September 2014, in a letter sent to the Security Council (UNSC), the United States asserted that:

Iraq has asked that the United States lead international efforts to strike ISIL sites and military strongholds in Syria in order to end the continuing attacks on Iraq, to protect Iraqi citizens, and ultimately to enable and arm Iraqi forces to perform their task of regaining control of the Iraqi borders.30

Two days later, the United Kingdom published a paper expressing its legal position, which reads as follows:

International law is clear that the use of force in international relations is prohibited, subject to limited exceptions. However, international law is equally clear that this prohibition does not apply to the use of military force by one State on the territory of another if the territorial State so requests or consents. It is clear in this case that Iraq has consented to the use of military force to defend itself against ISIL in Iraq.31

On 26 November 2014, the British authorities confirmed that their military measures constituted a ‘response to the request by the Government of Iraq for assistance in confronting the attack by the Islamic State in Iraq and the Levant (ISIL) on Iraq, contained in its letter to the President of the Security Council of 20 September 2014 (S/2014/691)’.32

Similar statements, notably by Canada,33 Australia,34 Norway,35 France,36 and Belgium,37 can be cited. It is true that all those states also invoked self-defence when they expanded the scope of their military operations to Syrian territory. Yet, with regard to their operations within Iraqi territory, it seems obvious that the consent given by Baghdad was considered a sufficient legal basis.

In parallel, the consent of Damascus was invoked as a legal basis justifying the military operations led by Russia within Syrian territory. In a letter to the UNSC, Russia explained that ‘in response to a request from the President of the Syrian Arab Republic, … [it had begun] launching air and missile strikes against the assets of terrorist formations in the (p. 879) territory of the Syrian Arab Republic on 30 September 2015’.38 Syria itself sent a letter specifying that

The Russian Federation has taken a number of measures in response to a request from the Government of the Syrian Arab Republic to the Government of the Russian Federation to cooperate in countering terrorism and to provide military support for the counter-terrorism efforts of the Syrian Government and the Syrian Arab Army … This support, which is being provided in response to a request from the Government of the Syrian Arab Republic, is fully consistent with international law, the Charter of the United Nations, international counter-terrorism instruments and Security Council resolutions 2170 (2014), 2178 (2014) and 2199 (2015), all of which reaffirm the unity, sovereignty and territorial integrity of the Syrian Arab Republic. The Syrian Arab Republic has repeatedly called on the international community to cooperate and coordinate with it fully and closely, whether in a multilateral or bilateral context, but those calls have fallen on deaf ears.39

For its part, Iran did not send a letter justifying its—more limited—military involvement in support of the Syrian authorities.40

Third states and international organizations did not question the legality of the military operations launched against ISIL respectively in Iraq and in Syria inasmuch as conducted with the consent of the respective governments. Some expressed criticism over violations of international humanitarian law perpetrated during the siege or the taking by some cities, like Aleppo in 2016,41 and Russia was occasionally criticized for having struck rebel groups other than ISIL.42 Nevertheless, the operations against this latter entity were never, as such, condemned as contrary to international law. By contrast, debates about the possibility to launch military operations without the consent of the relevant governmental authorities were particularly animated. This brings us to the second justification put forward by some intervening states in the context of the fight against ISIL.

2.  Self-defence

Self-defence was the main—and even the sole—argument used by the states that intervened on the Syrian territory without Damascus’ consent. It was also invoked by Turkey to justify a number of armed operations in Iraq that took place without the consent of the Baghdad Government. In both cases, this argument has raised some doubts and drew criticism from some states or international organizations. The UNSC, for its part, abstained from either endorsing or challenging self-defence in this particular case.

(p. 880) (a)  Self-defence as invoked by the intervening states to justify operations in Syria and Iraq

In the abovementioned letter to the UN, the United States developed their legal argument as follows:

ISIL and other terrorist groups in Syria are a threat not only to Iraq, but also to many other countries, including the United States and our partners in the region and beyond. States must be able to defend themselves, in accordance with the inherent right of individual and collective self-defence, as reflected in Article 51 of the Charter of the United Nations, when, as is the case here, the government of the State where the threat is located is unwilling or unable to prevent the use of its territory for such attacks. The Syrian regime has shown that it cannot and will not confront these safe havens effectively itself. Accordingly, the United States has initiated necessary and proportionate military actions in Syria in order to eliminate the ongoing ISIL threat to Iraq, including by protecting Iraqi citizens from further attacks and by enabling Iraqi forces to regain control of Iraq’s borders. In addition, the United States has initiated military actions in Syria against al-Qaida elements in Syria known as the Khorasan Group to address terrorist threats that they pose to the United States and our partners and allies.43

This statement, whose substance was reaffirmed later during the debates in the UNSC,44 suggests that self-defence would present two major characteristics. First, it would justify a use of force on the territory of a state (here Syria) that would be ‘unwilling or unable’ to put an end to the armed activities led against another state (here Iraq) by a non-state actor (here ISIL). Second, self-defence—whether individual or collective—could be justifiable as a preventive riposte both against an attack already launched (against Iraq) and to counter a ‘threat’ (against the United States and some of its allies).

Other US allies that invoked the right of self-defence seem to have shared globally the same position, even if it remains difficult to be sure to what extent. Three categories of states can be distinguished.

First, Turkey,45 Canada,46 and Australia expressly endorsed the ‘unwilling or unable’ argument (even if the two latter countries had previously expressed serious doubts in this respect47). For instance, Australia sent a letter to the UNSC according to which:

States must be able to act in self-defence when the Government of the State where the threat is located is unwilling or unable to prevent attacks originating from its territory. The Government of Syria has, by its failure to constrain attacks upon Iraqi territory originating from ISIL bases within Syria, demonstrated that it is unwilling or unable to prevent those attacks.48

(p. 881) Second, some European states seemed to propose a slightly different reasoning, which could be depicted as a ‘limited sovereignty’ argument. Thus, Germany observed that the Syrian Government did not exercise ‘effective control’ over some parts of its territory. Therefore, a right of self-defence was possible even without its consent, taking into account that the ‘measures [were] directed against ISIL, not against the Syrian Arab Republic’.49 Accordingly, Germany seemed to consider that self-defence could be justified in the absence of any form of responsibility from the Syrian state, because this state would have lost some part of its sovereignty, or at least could not exercise fully throughout its territory. This argument goes perhaps even further than the ‘unwilling or unable’ argument, the latter being based to some extent on a certain idea of a responsibility by the state concerned (this state having failed to execute its obligations to put an end to the activities of a terrorist group on its territory). Other states, like Norway50 or Belgium,51 adopted similar views. The case of France deserves particular scrutiny. In September 2015, this state invoked a ‘direct and extraordinary threat to the security of France’ to justify ‘actions involving the participation of military aircraft in response to attacks carried out by ISIL from the territory of the Syrian Arab Republic’.52 After the events of Paris of 13 November, which resulted in dozens of victims, France specified that it was the victim of an ‘armed aggression’ justifying a right to self-defence against ISIL.53 In an article published a few weeks later, François Alabrune, the main legal adviser of the Foreign Minister, specified how the French legal position could be interpreted.54 It appears from this article that France did not endorse the ‘unwilling or unable’ argument, and even that it remained in principle attached to a classical reading of Article 51 of the UN Charter, requiring an act of aggression perpetrated by a non-state actor to be attributed a state. However, given the exceptional character of the situation in Syria, France deemed it appropriate to cite the ICJ dictum in the Nuclear Weapons case, that is, an ‘extreme circumstance of self-defence, in which the very survival of a State would be at stake’.55

Third, some states invoked Article 51 in general terms only, without referring to any specific interpretation of that provision. The UK successively sent three letters in accordance with Article 51 of the UN Charter, mentioning a ‘necessary and proportionate’ exercise of the right of self-defence’,56 mainly due to the threat to international peace and (p. 882) security posed by ISIL. Denmark57 additionally referred to paragraph 5 of the above-cited UNSC Resolution 2249 (2015), in which the Council called upon states ‘to eradicate the safe haven that ISIL has established over significant parts of Iraq and Syria’. Finally, it must be noted that, on 17 November 2015, members of the EU agreed (for the first time) to activate Article 42.7 of the Treaty on European Union after the events of 13 November in France.58 This provision states:

If a Member State is the victim of armed aggression on its territory, the other Member States shall have towards it an obligation of aid and assistance by all the means in their power, in accordance with Article 51 of the United Nations Charter.

Overall, if all those states appear to share the same general argument, it is difficult to establish what their common interpretation of self-defence is, if any. Some have apparently denounced some form of responsibility of the Syrian state, which would have been ‘unwilling or unable’ to prevent ISIL from attacking the other states. Others prefer to argue that self-defence could be invoked against ISIL without any establishment of a form of responsibility of the Syrian state. Others are too general to enable us to specify what the scope and limit of self-defence would be in such a situation. Finally, France insists on the exceptional character of the situation. Furthermore, obvious discrepancies appear when considering the possibility to act in self-defence to counter a mere threat. Some have answered in the affirmative, either referring to a general threat (the United States, Canada, Australia) or evoking an ‘imminent threat’ (the United Kingdom and Turkey), whereas others, like France, Belgium, or Germany instead confined themselves to invoking the existence of an armed attack—and not a mere threat.59

Whatever the nuances between the positions of the intervening states could be, the question arises to what extent third states accepted the legality of the interventions as well as the specific legal interpretations put forward by the intervening states.

(b)  The ambiguous reaction by third states and international organizations

As mentioned above, during the first months after the launching of the US-led intervention in Syria, in September 2014, few debates took place at the UN level about its legality. This can be easily explained by the implicit coordination between all the states, including Syria, in their common fight against a common enemy: ISIL. However, when Russia decided to intervene directly at the end of the summer of 2015, the situation changed. Regardless of the political reasons that can explain this evolution, an assessment of the UN debates and the documents sent to the UN between 2014 and 2017 reveals a certain ambiguity. On the one hand, the intervention as such seems to have been approved, or at least gone unchallenged, by a vast number of states. On the other hand, it seems difficult to deduce from this muted reaction a common opinio juris supporting the legal arguments advanced by the intervening states.

(p. 883) What is clear is that, on some occasions, the ‘unwilling or unable’ argument was clearly rejected. Two different elements must be mentioned in this regard.

First, and as mentioned above, Turkey was one of the few states that explicitly endorsed this argument. It did so not only to justify crossing the Syrian boundary, but also the Iraqi one, more specifically as of the end of 2015.60 The reaction of the Baghdad authorities was unequivocal, as can be seen from the following letter sent to the UN:

On the evening of 3 December 2015, Turkish military forces comprising hundreds of soldiers and a number of tanks and armoured vehicles crossed the internationally recognized borders of Iraq … Those actions were taken without prior coordination or consultation with the federal Government of Iraq and are therefore in flagrant violation of the provisions and principles of the Charter of the United Nations. They also violate the territorial integrity and sovereignty of the Iraqi State, which are guaranteed by the provisions of the Charter, the principles of international law and the relevant Security Council resolutions, which reaffirm the independence, sovereignty and territorial unity and integrity of Iraq.61

A strong condemnation was also issued by the Arab League, with the adoption of a resolution entitled ‘Unified Arab position on the violation by Turkish forces of the sovereignty of Iraq’, in which the Council, after having recalled ‘the preservation of the sovereignty and territorial integrity of Member States and non-intervention in their internal affairs’, decided:

  1. 1.  to express its condemnation of the Turkish Government for its forces’ incursion into Iraqi territory, which is a violation of Iraqi sovereignty and a threat to Arab security;

  2. 2.  to demand that the Turkish Government immediately and unconditionally withdraw its forces from Iraqi territory;

  3. 3.  to support the Iraqi Government in any measures it may take in accordance with the relevant principles of international law to ensure that the Turkish Government withdraws its forces from Iraqi territory.62

Of course, the legal position of the Arab States is rather ambiguous. If they condemned Turkey for having violated the Charter through its incursion into Iraq, they nonetheless intervened themselves as members of the US-led coalition in Syria, without the consent of the government. Contrary to the other intervening states, they moreover did not send a letter to the UNSC or expressed any legal position during the debates within the UN. Their position about the exact scope of self-defence is therefore difficult to establish.63 It (p. 884) remains that the only legal stance about the unwilling and unable argument is, whatever the political reasons that can explain it, a strict condemnation of it.

Concerning the US-led intervention in Syria, it must first be observed that the Syrian state itself, after having been rather discrete during the first year of strikes against ISIL,64 officially denounced it as a violation of international law in various letters sent to the UN. On 21 September 2015, in a letter sent to the UNSC, it stated that ‘the United Kingdom, Australia and France … invoke a distorted reading of the intention of Article 51 of the Charter of the United Nations, one that is blatantly inconsistent with the Charter’,65 adding later that they ‘distort[ed] the provisions of the Charter and manipulate[d] international law’.66 Several other denunciations followed in subsequent months.67

Other states specifically denounced any military intervention led on Syrian territory without the consent of the Damascus Government. As of September 2014, Russia made it clear that such an action would be a ‘gross violation of the fundamental norms of international law’.68 Venezuela considered that ‘[t]he unilateral, imperialistic interventions we have witnessed have bypassed this Organization, [and] contravened the Charter’.69 Kazakhstan rejected the ‘illegal use of military force, including external foreign military interventions, which lead only to the destruction of statehood’,70whereas Cuba,71 (p. 885) Ecuador,72 Iran,73 India,74 and Argentina75 also denounced actions undertaken without the consent of the Syrian authorities.

Other states made more general statements, pointing to the necessity to respect the sovereignty of Syria. China insisted that it was ‘imperative to consistently comply with the purposes and principles of the Charter of the United Nations as well as the basic norms governing international relations, while maintaining the sovereignty, independence, unity and territorial integrity of Syria’.76 Brazil more generally observed that:

Time and again, we have seen the harmful effects of bending the rules and invoking exceptional rights in order to justify military interventions. Those strategies have enfeebled the multilateral system and aggravated the situation on the ground … The use of sanctions and military force should always be the last resort and, when it occurs, it must be in line with the provisions of the Charter of the United Nations. What we really need is better diplomacy to face the numerous challenges that still lie ahead.77

The United Arab Emirates stated that ‘we must respect the principles of the Charter on respect for sovereignty and non-interference, and refrain from any actions that could undermine the security and stability of countries. Foreign interventions, even under the pretext of settling conflicts, only create more violence and instability’.78 Algeria,79 Belarus,80 Angola,81 South Africa,82 Chad,83 and Bolivia84 expressed similar views.

In the end, a variety of reactions can be observed concerning the legality of the military actions allegedly undertaken pursuant to the right of self-defence. In this context, it is not surprising that the UN, and particularly the UNSC has been unable to reach a common position, as will be shown hereafter.

(c)  The ambiguities of the UNSC resolutions

The UNSC has never condemned the military operations launched against ISIL, whether in Iraq or in Syria. On the contrary, as already mentioned, it has ‘called upon [states] to take all necessary measures, in compliance with international law, in particular with the United Nations Charter … to eradicate the safe haven [ISIL] ha[s] established over significant parts of Iraq and Syria’.85 In a Declaration dated 19 September 2014, the Council had already ‘urge[d] the international community, in accordance with international law to further strengthen and expand support for the Government of Iraq as it fights ISIL and associated armed groups’.86 On 18 December 2015, the Council ‘reiterated’ its ‘call (p. 886) in resolution 2249 (2015) for Member States to prevent and suppress terrorist acts’ committed by ISIL.87

At the same time, while referring generally to the respect for international law and the UN Charter, the Council did not mention self-defence as such,88 an omission that can be understood given the criticisms made by certain states, including two of its permanent members.89 In this same resolution as in many others, the activities of ISIL have never been characterized as an ‘aggression’ or as an ‘armed attack’, but were rather qualified as a ‘threat’ to international peace.90 The Council has also insisted several times on the respect for the sovereignty and territorial integrity of Syria,91 and has ‘called upon Member States to cooperate and consistently support each other’s efforts to counter violent extremism’, and particularly ISIL.92

III.  Questions of Legality

The question of the legality of the war against ISIL has been highly debated in international scholarship. As we will be explained hereafter, some have supported the legality of the operations,93 whereas others expressed an opposite position by privileging a stricter conception of the jus contra bellum regime.94 Three different arguments have been debated, and will be examined in turn, namely consent, UNSC authorization and self-defence.

1.  Interventions based on invitations?

As mentioned, prior governmental consent has been invoked as a legal basis to justify two types of operations: those launched by the US-led coalition on Iraqi territory, on the one hand, and those led by Russia and Iran on Syrian territory, on the other hand. Conversely, this argument is not relevant when assessing the Turkish intervention in Iraq or the US-led intervention in Syria—both of which took place against the will of the two governments concerned.

It is generally recognized that a use of military force by a state on the territory of another state with the latter’s consent is not contrary to Article 2(4) of the UN Charter, which (p. 887) only prohibits a use of force by a state against another state.95 To be lawful, an intervention by invitation must however meet certain requirements. In its work dedicated to the Responsibility of the State, the International Law Commission asserted that:

the consent of the State must be valid in international law, clearly established, really expressed (which precludes merely presumed consent), internationally attributable to the State and anterior to the commission of the act to which it refers. Moreover, consent can be invoked as precluding the wrongfulness of an act by another State only within the limits which the State expressing the consent intends with respect to its scope and duration.96

At first sight, those conditions are unproblematic in our case, as it has been emphasized in legal doctrine.97 The Iraqi and Syrian authorities were, and are, recognized as representing their states, even if some have questioned their legitimacy, particularly given the serious human rights violations they are responsible for, and even if both had lost control over substantial parts of their respective territory.98 The Syrian Government still represents its state at the UN, as well as during the negotiations with opposition forces.99 Baghdad and Damascus have both given an express invitation to allied states to intervene on their respective territories to combat ISIL, and have never complained of an action that would have exceeded the limits of this invitation. Those elements probably explain why, as we observed above, the military operations based on consent have not been criticized by any state or international organization.100

On the other hand, the legality of those operations could be questioned on the basis of the principle, enunciated by the Institut de droit international and supported by a substantial part of legal doctrine,101 according to which ‘third States shall refrain from giving assistance to parties to a civil war which is being fought in the territory of another State’.102 The aim here is to reject any use of force directed against the right of self-determination of peoples, who must be able to freely determine their political status without outside interference.103 Nevertheless, no state or author has evoked this principle to criticize the foreign military operations against ISIL. This is probably explained by the fact that ISIL cannot be considered, in any circumstance, as representing the peoples of Iraq or Syria, wholly or in part.104 As explained above, and contrary to some other rebel groups operating in Syria, ISIL is unanimously considered as a terrorist organization. We are therefore in a situation similar to the Afghan or Malian cases,105 in which the fight against terrorism—with all the ambiguities that can result from this qualification—was invoked to justify military (p. 888) support to the governments without any legal constraints, at least from a jus contra bellum perspective.106 In this sense, when the UNSC ‘called upon’ states ‘to prevent and suppress terrorist acts’ committed by ISIL and to ‘eradicate’ its safe havens, it merely recognized that it is perfectly legitimate to support a government combating terrorists and thus confirmed the current state of customary international law.107

2.  Interventions authorized by the Security Council?

In Resolution 2249, the UNSC also called upon member states ‘to take all necessary measures, in compliance with international law, in particular with the United Nations Charter’ to pursue the abovementioned ends. The formula ‘all necessary means’ echoes previous resolutions in which the Council authorized military intervention in internal conflicts under Chapter VII of the Charter, such as in Somalia, Bosnia and Herzegovina, Rwanda, Haiti, Ivory Coast, or Libya, to mention just a few examples.108 It could be tempting to contend that such an authorization also existed in the Syrian case.109

Such an argument raises several problems, however. Different elements of concern have been mentioned in legal doctrine in this regard.110 First, the text of the resolution does not reveal a will of the Security Council to take any coercive measure according to Chapter VII. This chapter is not cited, as it has been in every previous situation where the use of force was authorized.111 And, more importantly, the Council has not ‘authorized’ (here again a word that is systematically used in the relevant precedents just cited) states to intervene on the territory of another state. Instead, it has ‘call[ed] upon’ states to act, with international law, in particular with the United Nations Charter. This expression suggests that states are urged to act, but according to an existing legal basis, which could be the consent of the states concerned or self-defence. In both cases, the resolution does not provide anything more, from a legal point of view.

Second, examining the records of the debates which preceded the adoption of the resolution, it is clear that the thesis of an ‘authorization’ was never evoked. Russia stated that the resolution was:

a political appeal, rather than a change to the legal principles underlying the fight against terrorism. We consider it a step in creating a broad anti-terrorism front by marshalling comprehensive cooperation among all States to end all manifestations of terrorism and eradicate its root causes.112

Nigeria considered that urgent action against ISIL was called for, and that the resolution ‘provides a framework for achieving that’ purpose,113 and the United Kingdom affirmed (p. 889) that it is ‘a powerful international recognition of the threat ISIL poses. It calls for lawful action’.114 By comparison, previous debates surrounding the adoption of resolutions that effectively authorized a use of force leave no doubt about the will to use Chapter VII powers to offer a proper legal basis.115 Third, and related, subsequent practice confirms this restrictive interpretation. As mentioned above, the Council later ‘[r]eiterat[ed] its call in resolution 2249’, without mentioning either an authorization, or even the ‘necessary measures’ formula. More importantly, if several states cited Resolution 2249 (2015) for supporting their actions against ISIL in self-defence,116 they never invoked it as a genuine legal basis.117 This is perfectly understandable. To argue that the legal basis of the military action should be found in this UNSC resolution would have amounted to an implicit recognition that, before its adoption, the military operations in Syria undertaken without the consent of the Syrian Government were illegal. Western powers obviously were not eager to follow that path, and they consequently preferred to use Resolution 2249 (2015) as a political blessing rather than as a specifically legal element.

In the end, by requiring states to act ‘in compliance with international law, in particular with the United Nations Charter’, the Council did not ‘authorize’ any military action, but allowed states to maintain their respective (and opposed) positions. For Syria, Russia, Iran, and other states, this ‘compliance’ implied action in coordination with the Syrian authorities, with the latter’s consent offering a clear and uncontested legal basis. By contrast, for the United States and its allies, it meant that self-defence according to Article 51 of the UN Charter was, and continued to be seen, as the proper legal basis. A basis that is nonetheless debatable in positive international law.

3.  Actions in self-defence according to Article 51 of the UN Charter?

As explained above, several states have invoked self-defence to justify the bombing of ISIL on Syrian territory. We have also observed that this argument has been interpreted differently, which leads us to examine successively the ‘unwilling or unable’, the ‘limited sovereignty’, and the ‘self-help’ arguments, followed by a brief reflection about the question of individual or collective self-defence, particularly in relation to the question of anticipatory self-defence.

(a)  The ‘unwilling or unable’ argument

As specified above, the United States and some of its allies have argued that, since Syria was ‘unwilling or unable’ to put an end to ISIL’s cross-border armed activities, self-defence could justify a military riposte on its territory. Here, the United States supports (p. 890) an argument that had been proposed in literature in view of a certain (limited) prior state practice.118 But can this argument be convincingly invoked in the Syrian case?

According to the Declaration of Friendly Relations annexed to UNGA Resolution 2625 (XXV) adopted in 1970:

Every State has the duty to refrain from organizing, instigating, assisting or participating in acts of civil strife or terrorist acts in another State or acquiescing in organized activities within its territory directed towards the commission of such acts … no State shall organize, assist, foment, finance, incite or tolerate subversive, terrorist or armed activities directed towards the violent overthrow of the regime of another State, or interfere in civil strife in another State …119

This rule, considered as reflecting customary international law,120 implies that, if a state assists or participates in terrorist acts, or even simply tolerates them, it will bear a responsibility for a breach of the prohibition on the use of force enshrined in Article 2(4) of the UN Charter.

This does not mean, however, that the Friendly Relations Declaration renders support to the argument put forward by the United States in the Syrian case.121 Two different elements must be pointed out in this regard.

First, it must be stressed that the rule only prohibits a certain unwillingness by a given state, which would either act in support of a terrorist group, or would at least ‘tolerate’ its activities. An action (but also some forms of inaction) can therefore be sufficient to establish a use of force in breach of the Charter. However, in both cases, a certain level of complicity seems to be required. The scheme could be illustrated by reference to the relations between Al Qaeda and the Taliban regime before the war triggered by the United States in October 2001, or between Hezbollah and Lebanon before the war launched by Israel in July 2006.122 By contrast, the Syrian regime has effectively combatted ISIL for years, as confirmed in several reports of the UN Secretary-General.123 Against this background, it would be excessive to contend that it was ‘unwilling’ to put an end to the terrorist activities of this group, either by assisting, or even by tolerating it.124 Yet, it has been argued that the Syrian regime was ‘unable’ to prevent cross-border operations by ISIL, an argument that is factually undeniable. However, a mere ‘inability’ cannot lead to any form of responsibility for a state whose territory is used by irregular bands, as the International Court of Justice made clear in Armed Activities on the territory of the Congo. In its first counterclaim, (p. 891) Uganda had contended that ‘it ha[d] been the victim of military operations and other destabilizing activities carried out by hostile armed groups based in the DRC … and either supported or tolerated by successive Congolese governments’.125 The Court rejected the argument, considering that:

The DRC was thus acting against the rebels, not in support of them. It appears, however, that, due to the difficulty and remoteness of the terrain discussed in relation to the first period, neither State was capable of putting an end to all the rebel activities despite their efforts in this period. Therefore, Uganda’s counter-claim … must fail.126

As confirmed by the Court, the mere inability or lack of success cannot be equated with any breach of international law, which rather refers to a ‘due diligence’ principle, equivalent to an obligation of means, and not an obligation of result. If we transpose this to our case, the mere fact that neither Syria nor Russia, nor, for that matter, the members of the US led-coalition, have been able to prevent ISIL from pursuing its activities is not a sufficient element to challenge the responsibility of any of those states, including Syria itself. Quite the opposite, if we follow what the Court said, it appears that an inability a priori seems to show that there has been no violation at all.

Second, even if, for the sake of the argument, one were to presume that a violation of the duty of vigilance could be observed, that mere conclusion would not imply, as such, an activation of the right of self-defence pursuant to Article 51 of the UN Charter. According to that provision, self-defence is triggered if ‘an armed attack occurs’ and, as it is generally recognized,127 an ‘armed attack’ requires something more than a mere ‘use of force’. As recognized by the ICJ:

[W]hile the concept of an armed attack includes the despatch by one State of armed bands into the territory of another State, the supply of arms and other support to such bands cannot be equated with armed attack. Nevertheless, such activities may well constitute a breach of the principle of the non-use of force and an intervention in the internal affairs of a State, that is, a form of conduct which is certainly wrongful, but is of lesser gravity than an armed attack.128

Article 3(g) of the definition of aggression annexed to UNGA Resolution 3314 (XXIX) specifies that the situation could be different if a state either ‘sent’ an irregular group to the territory of another state, or was ‘substantially involved’ in a particular use of force perpetrated by this group. This provision was systematically applied by the ICJ—and by states appearing before it—whenever it was confronted to a ‘triangular relation’ between a territorial state, an irregular group operating from this state, and a victim state targeted by this group.129 It has also been considered as relevant in 2010, when the Assembly of States Parties of the ICC defined the crime of aggression.130 If we transpose it to our case, it is obvious that no right of self-defence could be established, as the Syrian state neither ‘sent’ ISIL abroad, nor was it ‘substantially involved’ in the armed activities of this non-state actor.131

(p. 892) Third, it must be pointed out that the ‘unwilling or unable’ test, even if accepted in theory, is difficult to invoke when the territorial state is ready to give its consent. As a matter of principle, the authors supporting this test generally consider that:

the victim state’s preference in each case should be to obtain the consent of the territorial state … the victim state should, as a rule, explore whether there is an opportunity to work cooperatively with the territorial state to suppress the threat.132

This element was simply ignored by the United States in the Syrian case. For political reasons (due to the strong opposition between Damascus and Washington), consent was never requested, if it was ever envisaged in the first place. It is thus clear that the US interpretation of the ‘unwilling or unable’ argument is far broader than that which is suggested by its advocates; even measured against the criteria set out by scholars who support this test, the US interpretation seems unconvincing.133

All in all, it is not surprising that the ‘unwilling or unable’ argument has not been accepted by a large number of states.134 As mentioned, even some allies of the United States preferred to refer instead to other concepts such as ‘limited sovereignty’ or ‘self-help’, even though these concepts equally raise considerable problems in international law.

(b)  The ‘limited sovereignty’ argument

As observed earlier, states such as Germany seemed to consider that the military actions in Syrian territory were only directed against ISIL, and not against the Syrian state itself. This state, by having lost control over part of its territory, would not be entitled to invoke its sovereignty to oppose a use of force. Against this background, the invocation of self-defence against ISIL would be sufficient to justify an armed intervention on the Syrian territory.

Such an argument is obviously incompatible with the most basic elements of the jus contra bellum regime enshrined in the UN Charter. Suffice it to cite the following two excerpts from UNGA resolutions considered to reflect international customary law:

Every State has the duty to refrain from the threat or use of force to violate the existing international boundaries of another State or as a means of solving international disputes …135

[aggression can be defined as an] attack by the armed forces of a State of the territory of another State [or a] Bombardment by the armed forces of a State against the territory of another State or the use of any weapons by a State against the territory of another State.136

In other words, when a state crosses the boundary of another state with military units or airplanes and bombs its territory, it uses force in ‘international relations’, according to Article 2(4) of the UN Charter.137 This is even more obvious when it causes death among the nationals of that state and destroys its public goods and infrastructure, as has (p. 893) been the case in Syria.138 Consequently, Syria has unsurprisingly protested and has repeatedly ‘demand[ed] compensation from the American Government and its ally States for the deliberate destruction of Syrian economic and oil installations’.139 Given those factual and legal elements, it would be absurd to reject any form of responsibility simply by arguing that the strikes did not target the Syrian authorities as such. In international law, a state is composed of a government but also of a territory and a population. And, more generally, the Charter is entirely based on the concept of ‘sovereign equality’, which implies that every state is fully sovereign and can invoke its territorial integrity to oppose any use of force—particularly when it is equivalent to a massive bombing—by another state.140 This is precisely one of the changes that the Charter has brought by comparison with previous historical periods, in which some states were ‘more equal and sovereign’ than others, and could just refer to their ‘vital interests’ to justify a military intervention.141

(c)  The ‘necessity’ or ‘self-help’ argument

As previously stated, the United Kingdom and some other European states simply referred to the necessity or the proportionality criteria as supporting their argument of self-defence, without further elaboration. The reasoning seems to be the following: when a state is threatened or attacked by a non-state actor, it can use self-defence against it, provided that it is ‘necessary,’ even if it implies bombing the territory of another state, killing some of its nationals, and destroying some of its public goods. Here, we seem to be faced with a sort of revival of the self-help argument, frequently used by powerful states in the nineteenth century to justify their military action, an impression supported by the reference to the Caroline incident (1837) regularly invoked by certain authors.142

Three factors must be considered at this stage, which seriously challenge such an argument, both in general terms and in the Syrian case.

First, as confirmed by the ICJ jurisprudence, the jus contra bellum regime remains essentially state-centric. Of course, one could argue that Article 51 is broadly defined, and (p. 894) does not require that the author of the ‘armed attack’ would be a state.143 However, that would not permit any state to launch a military operation against the territory of another state, as it has been the case in Syria. As exposed just above, every state is entitled to invoke its sovereignty and its territorial integrity. In other words, Article 2(4) of the UN Charter remains applicable and prohibits a use of force by state A on the territory of state B, except if state A can invoke self-defence, but vis-à-vis the state it has decided to attack, meaning state B.144 However, in this hypothesis, it will imply that one has to establish some form of responsibility of state B, and even prove that it has been the author of an ‘armed attack’, directly or indirectly (by sending the terrorist group against state a or by having been substantially involved in its activities).145

Second, it must be recalled that, in contemporary international law, ‘necessity’ is not recognized as a separate legal basis justifying a use of force.146 Article 51 is very clear in this regard, as it requires on the one hand the existence of an armed attack and, on the other—even if this is mainly a requirement deduced from customary law—a condition of necessity and proportionality. This latter criterion is not considered as opening a right to self-defence, but as restraining its exercise. As the Court stated in the Armed Activities case:

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.147

Obviously, in the aftermath of the Iraqi war, the Court was eager to affirm that a ‘self-help’ argument could jeopardize the contemporary prohibition on the use of force.

Third, even if we limit our analysis to an assessment of a ‘necessity’ criterion in the case at hand, the most convincing conclusion would still be the illegality of the military operations led on the Syrian territory. It must be recalled that the Syrian authorities made clear that they were ready to cooperate with other states in the common fight against ISIL.148 This shows that a state is never ‘unable’ to act, as it can either take itself military action or accept that other states intervene on its own territory.149 Actually, in the case at hand, both options were chosen by the Syrian Government. The result is that it becomes totally unpersuasive to evoke a ‘necessity of self-defence’, ‘instant, overwhelming and leaving no choice of means, and no moment for deliberation’,150 particularly if we know that this criterion has been strictly defined by the Court as being ‘strict and objective, leaving no room for any “measure of discretion” ’.151

For all those reasons, it is difficult to avoid the conclusion that self-defence could not justify the unilateral strikes against Syria.

(p. 895) Finally, some problems in relation to the individual or collective character of self-defence must be evoked.

(d)  Individual or collective self-defence?

As explained above, most states invoked the right of ‘collective’ self-defence, basically to support Iraq in its fight against ISIL. Some of the states participating in the US-led coalition moreover referred to their individual right to self-defence, due to a specific armed attack but also a threat they had allegedly suffered. In both cases, questions arise concerning the legal validity of the argument.

Concerning the collective dimension, it is interesting to note that Iraq never sent a letter to the UNSC according to Article 51 of the UN Charter, as required by this provision when a state invokes self-defence. The two letters exposed above both contain an invitation to intervene against ISIL, but none of them refer to Article 51 or to self-defence specifically. Yet, as the Court has said, it is ‘evident that if the victim State wishes another State to come to its help in the exercise of the right of collective self-defence, it will normally make an express request to that effect’.152 In the case at hand, no express request has been made to act in self-defence, at least as far as Iraq is concerned.153 By contrast, when the European states decided to support France after the 13 November events in Paris, no legal problem arose.

In this latter case, it is also obvious that France could, as a matter of principle—and thus independently of the problems mentioned above—invoke individual self-defence. Some other states, like the United States or the United Kingdom, have nonetheless also invoked individual self-defence on account of their facing a ‘threat’, whether general (in the former case) or ‘imminent’ (in the latter).154 The argument of a preventive, pre-emptive, or anticipatory self-defence, whatever its name, is highly controversial in contemporary international law.155 Article 51 of the UN Charter expressly requires the existence of an armed attack, even if it leaves the door open to a flexible interpretation as to determining the moment when the armed attack begins.156 An assessment of the practice of states does not lead to another conclusion. Proponents of anticipatory self-defence often refer to the Caroline precedent157 but, even if we consider as relevant a case dating back from 1837 for purposes of ascertaining the legal regime governing the use of force in the twenty-first century, a serious problem remains: the ‘preventive’ character of self-defence was neither mentioned nor evoked in the Webster formula, nor relevant in the factual context (which rather reveals that the Caroline incident was only one of a larger range of incursions that (p. 896) had already been observed from US territory into then British Canada).158 More importantly, it is highly significant that, in 2005, during the debates that took place in the UN regarding the interpretation of the Charter rules, a proposal including a right of self-defence to counter an imminent threat had been introduced in the text elaborated by the Secretary-General and submitted to states.159 However, the majority of states refused to accept any alteration of the text of Article 51,160 and the passage opening the door to some limited form of anticipatory self-defence was consequently deleted in the final text of UNGA Resolution 60/1.161 In sum, and in conformity with the practice posterior to the adoption of the Charter, the preventive or pre-emptive self-defence argument has never been accepted by the international community of states as a whole.162 As a result, invoking it in the Syrian case, particularly in the broad version used by the United States, appears highly problematic.

IV.  Conclusion: Precedential Value

The military operations against ISIL have given rise to intense controversies, not only between states but also between scholars. It is therefore difficult to invoke it as a precedent in favour of any particular interpretation of the jus contra bellum rules.163

This is not necessarily the case for all its aspects, however. To a certain extent, the war against ISIL could be seen as a confirmation of the possibility to intervene in internal conflicts in support of a government. This possibility seems hardly limited by the principle of non-intervention in civil wars, which can be easily circumvented by qualifying the rebels as ‘terrorists’.164 In the case of ISIL, that does not appear problematic, given the very nature of this entity. However, if we put this precedent together with others like the French intervention in Mali165 or to a lesser extent the Saudi-led intervention in Yemen,166 it could be questioned if we are not witnessing a shift challenging the classical principle of neutrality of international law in internal conflicts.167

Some states have extensively but also incoherently invoked self-defence. Given the reluctant, or at least prudent reactions by other states, it would be premature to conclude to an evolution or new interpretation of the scope and meaning of Article 51 of the UN (p. 897) Charter.168 The current state, and a fortiori the future, of international law seems rather uncertain in this field. During the war in Afghanistan, the self-defence argument had been overwhelmingly approved by states, even with some limited reservations.169 By contrast, this same argument was strongly contested after the war launched by Israel in Lebanon, qualified as an act of aggression by the majority of states.170 The war against ISIL lies probably somewhere between those two precedents: self-defence has been neither widely contested, nor approved. In this context, it is difficult not to mention the constant position of the non-aligned movement, composed of 120 states, which reiterated on several occasions in the context of the war against ISIL that:

consistent with the practice of the UN and international law, as pronounced by the ICJ, Article 51 of the UN Charter is restrictive and should not be re-written or re-interpreted.171

This clearly shows that the majority of states is not ready to accept the ‘unwilling or unable’, ‘limited sovereignty’, or ‘self-help’ necessity arguments, or, for that matter, the permissibility of preventive or pre-emptive self-defence, which would undoubtedly imply at the very least a new interpretation of the UN Charter.172 Similarly, it seems that many scholars do not share the view according to which international law would have recognized a broad conception of self-defence.173 More than 300 authors, among which major specialists of the jus contra bellum have signed the following text, during the summer of 2016:

For several years now, the number of terrorist attacks has been on the rise, including in Western countries. Many have equated these attacks with acts of war, requiring an immediate reaction in self-defence by States using military force, either individually or collectively in coalitions set up for that purpose. Thus, numerous military interventions have been conducted in the name of self-defence, including against Al Qaeda, ISIS or affiliated groups. While some have downplayed these precedents on account of their exceptional nature, there is a serious risk of self-defence becoming an alibi, used systematically to justify the unilateral launching of military operations around the world. Without opposing the use of force against terrorist (p. 898) groups as a matter of principle— particularly in the current context of the fight against ISIS—we, international law professors and scholars, consider this invocation of self-defence to be problematic.174

This is not say that the evolution in favour of a broader conception of self-defence could not become more accepted in the following years. In the jus contra bellum domain like in others, it would be imprudent to exclude any future evolution of opinio juris.

Footnotes:

1  This chapter is a substantially revised version of the following articles: ‘The “Unwilling or Unable” Theory: Has it Been, and Could It Be, Accepted?’ (2016) 29 Leiden Journal of International Law 777–99; ‘L’argumentation des Etats européens pour justifier une intervention militaire contre l’ “Etat islamique” en Syrie: vers une reconfiguration de la notion de légitime défense?’ (2016) 49 Revue belge de droit international 31–67. The chapter was finished on 28 April 2017. All website references were last accessed on this date. Thanks to Tom Ruys for his critical and useful remarks on a former draft of this text.

2  (2014) Keesing’s Record of World Events 53340–41.

3  See the relevant resolutions adopted by the Security Council on the issue, cited below.

4  See, generally, Patrick Cockburn, The Rise of Islamic State: ISIS and the New Sunni Revolution (Verso Books 2015); Michael Weiss and Hassan Hassan, ISIS: Inside the Army of Terror (Regan Arts 2015). See Chapter 49, ‘The Iraq War—2003’ by Marc Weller in this volume.

5  See, eg, Iraq crisis: ‘How Saudi Arabia Helped Isis Take Over the North of the Country’ The Independent (London, 13 July 2014); ‘Research Paper: ISIS-Turkey Links’ The Huffington Post (8 September 2016).

6  (2014) Keesing’s Record of World Events 53494–95; See Tom Ruys, Nele Verlinden, Marie Aronsson, Russell Buchan, Patrick Butchard, Kenneth Chan, Jessica Dorsey, Ben Murphy, and Sten Verhoeven, ‘Digest of State Practice 1 January–30 June 2014’ (2014) 1 Journal on the Use of Force and International Law 356; Tom Ruys and Nele Verlinden, ‘1 July–31 December 2014’ (2014) 2 Journal on the Use of Force and International Law 131–32.

7  (2014) Keesing’s Record of World Events, 53535–36, 53441.

9  See, eg, the positions expressed by several states during the debates within the Security Council: UNSC Verbatim Records (19 September 2014) UN Doc S/PV.7271 and (24 September 2014) UN Doc S/PV.7272. Concerning the United States see also: ‘Statement by the President on ISIL’, The White House—Office of the Press Secretary (10 September 2014) <https://obamawhitehouse.archives.gov/the-press-office/2014/09/10/statement-president-isil-1>.

10  Anne-Laure Chaumette, ‘Daech, un “Etat” islamique?’ (2014) LX Annuaire français de droit international 71–89; Olivia Flasch, ‘The Legality of the Air Strikes Against ISIL in Syria: New Insights on the Extraterritorial Use of Force Against Non-State Actors’ (2016) Journal on the Use of Force and International Law 11; Olivier Corten, ‘L’“Etat islamique”, un Etat? Enjeux et ambiguïtés d’une qualification juridique’ in Farah Safi et Arnaud Casado (eds), Daech et le droit (Panthéon-Assas 2016) 53–70.

11  Letter dated 25 June 2014 from the Permanent Representative of Iraq to the United Nations addressed to the Secretary-General (25 June 2014) UN Doc S/2014/440.

12  Letter dated 20 September 2014 from the Permanent Representative of Iraq to the United Nations addressed to the President of the Security Council (22 September 2014) UN Doc S/2014/691.

13  See the official site of Ministère des Armées; ‘Opération Chammal’ at <http://www.defense.gouv.fr/operations/operations/irak-syrie/dossier-de-presentation-de-l-operation-chammal/operation-chammal>.

14  See Ministry of Defence, ‘Operation Shader, Two Years On’ <https://social.shorthand.com/DefenceHQ/3g2nIMeQu6/operation-shader>.

15  ‘On Eve of Security Council Summit, Ban Calls for Decisive Action Against Terrorism’ UN News Centre (23 September 2014) <http://www.un.org/apps/news/story.asp?NewsID=48796#.WJhsmBQ1epc>.

16  See the official site of ‘Operation Inherent Resolve’ <http://www.inherentresolve.mil>.

17  Report of the Secretary-General on the implementation of Security Council Resolutions 2139 (2014) and 2165 (2014) (23 October 2014) UN Doc S/2014/756, [14].

18  See notably Australia (Australian Prime Minister Interview of 16 September 2014) reproduced in <https://iusadbellum.files.wordpress.com/2011/07/etatislamique2015.pdf>) and Canada (Canadian Minister of Foreign Affairs, ‘Government Orders—Military Contribution Against ISIL’, in House of Commons Debates, 41th Legislature, 2nd session, No 123, Parliament of Canada, 6 October 2014). Other states are also cited by Tom Ruys and Luca Ferro, ‘Divergent Views on the Content and Relevance of the Jus ad Bellum in Europe and the United States? The Case of the U.S.-Led Military Coalition Against “Islamic State” ’ in Chiara Giorgetti and Guglielmo Verdirame (eds), Concepts on International Law in Europe and the United States (CUP 2017).

20  Identical letters dated 25 May 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (1 June 2015) UN Doc A/69/912–S/2015/371.

21  See, eg, Reports of the Secretary General (24 September 2014) UN Doc S/2014/696; (23 March 2015) UN Doc S/2015/206; (17 April 2015) UN Doc S/2015/264; (23 July 2015) UN Doc S/2015/561.

22  ‘U.S. Rules Out Coordinating with Assad on Airstrikes Against Islamists in Syria’ Washington Post (Washington DC, 26 August 2014).

23  However, repeated criticism was made by Bashar el Assad in some interviews or press statements; see, eg, ‘L’entretien intégral—Le Président syrien Bachar El-Assad reçoit Paris Match’ Paris Match (Paris, 4 December 2014) <http://www.parismatch.com/Actu/International/Le-president-syrien-Bachar-el-Assad-recoit-Paris-Match-661934>.

24  See, eg, Identical letters dated 25 May 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (1 June 2015) UN Doc S/2015/371.

25  Letter dated 15 October 2015 from the Permanent Representative of the Russian Federation to the United Nations addressed to the President of the Security Council (15 October 2015) UN Doc S/2015/792. See (2015) Keesing’s Record of World Events 54284–85.

26  UNSC Res 2249 (2015) (20 November 2015) UN Doc S/RES/2249 (2015), at [5].

27  See, eg, Third report of the Secretary-General on the threat posed by ISIL (Da’esh) to international peace and security and the range of United Nations efforts in support of Member States in countering the threat (30 September 2016) UN Doc S/2016/830, at 2–3, [3]–[7].

28  For other interesting statements, see Tom Ruys and Nele Verlinden, ‘1 July–31 December 2014’ (2015) 2 Journal on the Use of Force and International Law 140–45; Tom Ruys, Nele Verlinden, and Luca Ferro, ‘Digest of State Practice 1 January–30 June 2015’ (2015) 2 Journal on the Use of Force and International Law 280–83; Tom Ruys, Luca Ferro, and Nele Verlinden, ‘1 July–31 December 2015’ (2016) 3 Journal on the Use of Force and International Law 141–56; Tom Ruys, Luca Ferro, and Nele Verlinden, ‘Digest of State Practice 1 July–31 December 2015’ (2016) 3 Journal on the Use of Force and International Law 317–19.

29  This overview results from an exhaustive examination of all the records of the debates which took place in the UN between January 2014 and 15 January 2017, as well as of the documents sent to the UN during this period.

30  Letter dated 23 September 2014 from the Permanent Representative of the United States of America to the United Nations addressed to the Secretary-General (23 September 2014) UN Doc S/2014/695; see also UN Doc S/PV.7271 (n 9) 16.

31  ‘Summary of the government legal position on military action in Iraq against ISIL’ (25 September 2014) available at <https://www.gov.uk/government/publications/military-action-in-iraq-against-isil-government-legal-position/summary-of-the-government-legal-position-on-military-action-in-iraq-against-isil>.

32  Identical letters dated 25 November 2014 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the Secretary-General and the President of the Security Council (26 November 2014) UN Doc S/2014/851.

33  Letter dated 31 March 2015 from the Chargé d’affaires a.i. of the Permanent Mission of Canada to the United Nations addressed to the President of the Security Council (31 March 2015) UN Doc S/2015/221.

34  Letter dated 9 September 2015 from the Permanent Representative of Australia to the United Nations addressed to the President of the Security Council (9 September 2015) UN Doc S/2015/693; UN Doc S/PV.7272 (n 9) 15.

35  Letter dated 3 June 2016 from the Permanent Representative of Norway to the United Nations addressed to the President of the Security Council (3 June 2016) UN Doc S/2016/513.

36  UN Doc S/PV.7271 (n 9) 12–13.

37  Letter dated 7 June 2016 from the Permanent Representative of Belgium to the United Nations addressed to the President of the Security Council (9 June 2016) UN Doc S/2016/523.

38  Letter dated 15 October 2015 from the Permanent Representative of the Russian Federation to the United Nations addressed to the President of the Security Council (15 October 2015) UN Doc S/2015/792; see also UNSC Verbatim Record (30 September 2015) UN Doc S/PV.7527, 4.

39  Identical letters dated 14 October 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (16 October 2015) UN Docs A/70/429 and S/2015/789.

40  See Ruys et al (n 6) 351.

41  See, eg, Amnesty International in its annual Report 2015/2016 <https://www.amnesty.org/en/countries/middle-east-and-north-africa/syria/report-syria/)>.

42  UNGA Third Committee, Situation of Human Rights in the Syrian Arab Republic (2 November 2015) UN Doc. A/C.3/70/L.47, [15]; ‘Council conclusions on Syria’, Council of the European Union (12 October 2015); Tom Ruys, Luca Ferro, and Nele Verlinden, ‘Digest of State Practice 1 July–31 December 2015’ (2016) 3 Journal on the Use of Force and International Law 154–56. See also the denunciations made by the National Coalition of Syrian Revolution and Opposition Forces; annexed to Letter dated 1 October 2015 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the President of the Security Council (1 October 2015) UN Doc S/2015/750.

43  Letter dated 23 September 2014 from the Permanent Representative of the United States of America to the United Nations addressed to the Secretary-General (23 September 2014) UN Doc S/2014/695.

44  UNSC Verbatim Record (20 November 2015) UN Doc S/PV.7565, 4.

45  Letter dated 24 July 2015 from the Chargé d’affaires a.i. of the Permanent Mission of Turkey to the United Nations addressed to the President of the Security Council (24 July 2015) UN Doc S/2015/563. See also Identical letters dated 22 February 2015 from the Permanent Representative of Turkey to the United Nations addressed to the Secretary-General and the President of the Security Council (23 February 2015) UN Doc S/2015/127 and Letter dated 19 February 2016 from the Permanent Representative of Turkey to the United Nations addressed to the President of the Security Council (19 February 2016) UN Doc S/2016/163.

46  Letter dated 31 March 2015 from the Chargé d’affaires a.i. of the Permanent Mission of Canada to the United Nations addressed to the President of the Security Council (31 March 2015) UN Doc S/2015/221.

47  See reference above, n 18.

48  Letter dated 9 September 2015 from the Permanent Representative of Australia to the United Nations addressed to the President of the Security Council (9 September 2015) UN Doc S/2015/693. See also UN Doc S/PV.7527 (n 38) 69.

49  Emphasis added, Letter dated 10 December 2015 from the Chargé d’affaires a.i. of the Permanent Mission of Germany to the United Nations addressed to the President of the Security Council (10 December 2015) UN Doc S/2015/946.

50  Letter dated 3 June 2016 from the Permanent Representative of Norway to the United Nations addressed to the President of the Security Council (3 June 2016) UN Doc S/2016/513.

51  Letter dated 7 June 2016 from the Permanent Representative of Belgium to the United Nations addressed to the President of the Security Council (9 June 2016) UN Doc S/2016/523.

52  Identical letters dated 8 September 2015 from the Permanent Representative of France to the United Nations addressed to the Secretary-General and the President of the Security Council (9 September 2015) UN Doc S/2015/745.

53  UN Doc S/PV.7565 (n 44) 2.

54  François Alabrune, ‘Fondements juridiques de l’intervention militaire française contre Daesh en Irak et en Syrie’ (2016) 120 Revue générale de droit international public 9–10. See the comments by Franck Latty, ‘Le brouillage des repères du jus contra bellum. À propos de l’usage de la force par la France contre Daech’ (2016) 120 Revue générale de droit international public, 28–29 and Karine Bannelier-Christakis, ‘The Joint Committee’s drones report: Far-Reaching Conclusions On Self-Defence Based on a Dubious Reading of Resolution 2249’ (2016) 3 Journal on the Use of Force and International Law 224.

55  Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep, at 266, [105].

56  Identical letters dated 25 November 2014 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the Secretary-General and the President of the Security Council (26 November 2014) UN Doc S/2014/851; Letter dated 7 September 2015 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the President of the Security Council (7 September 2015) UN Doc S/2015/688; Letter dated 3 December 2015 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the President of the Security Council (3 December 2015) UN Doc S/2015/928.

57  Letter dated 11 January 2016 from the Permanent Representative of Denmark to the United Nations addressed to the President of the Security Council (13 January 2016) UN Doc S/2016/34.

58  Council of the EU, Outcome of The Council Meeting, 3426th Council meeting, Foreign Affairs (Brussels, 16 and 17 November 2015) 14120/15. See François Gouttefarde, ‘L’invocation de l’article 42.7 TUE ou la solidarité militaire européenne à l’épreuve de la guerre contre le terrorisme’ (2016) 120 Revue générale de droit international public 51–67.

59  See the relevant letters and references mentioned above, nn 49, 51, and 52.

60  See also Identical letters dated 28 October 2016 from the Permanent Representative of Turkey to the United Nations addressed to the Secretary-General and the President of the Security Council (1 November 2016) UN Doc S/2016/912.

61  Letter dated 11 December 2015 from the Permanent Representative of Iraq to the United Nations addressed to the President of the Security Council (14 December 2015) UN Doc S/2015/963; see also a similar condemnation after a new incursion by Turkish forces in Annex to the Identical letters dated 17 October 2016 from the Permanent Representative of Iraq to the United Nations addressed to the Secretary-General and the President of the Security Council (19 October 2016) UN Doc S/2016/870.

62  Letter dated 7 January 2016 from the Permanent Representative of Egypt to the United Nations addressed to the President of the Security Council (11 January 2016) UN Doc S/2016/16, copy of resolution No. 7987 adopted at the Ministerial Meeting of the Council of the League of Arab States, held on 24 December 2015, and entitled ‘Unified Arab position on the violation by Turkish forces of the sovereignty of Iraq’ (see annex). A similar position seems to have been reiterated a few months later, in Resolution 653 adopted by the Arab League at its twenty-seventh ordinary session at the summit level on 25 July 2016 in Nouakchott, see Annex to the Identical letters dated 17 October 2016 from the Permanent Representative of Iraq to the United Nations addressed to the Secretary-General and the President of the Security Council (19 October 2016) UN Doc S/2016/870.

63  In 2013, the Arab League had affirmed ‘the right of each member state, in accordance with its wish, to provide all means of self-defense, including military support to back the steadfastness of the Syrian people and the free army’ (24th Arab Summit Issues Doha Declaration, 26 March 2013) <http://arableaguesummit2013.qatarconferences.org/news/news-details-17.html>; see also, more implicitly, Letter dated 3 February 2016 from the Permanent Representative of Qatar to the United Nations addressed to the President of the Security Council (5 February 2016) UN Doc S/2016/111. This seems to recover a very broad conception of self-defence as applicable in internal conflicts. Whatever it could mean, and independently of the considerable legal problems this position raises, it must be observed that it does not concern the fight against ISIL as such.

64  See, however, some statements insisting on the necessity of cooperation, in general terms: UN Doc S/PV.7271 (n 9) 43; UNSC Verbatim Record (19 November 2014) UN Doc S/PV.7316, 33. Syria has also condemned the Turkish military intervention, rejecting specifically the argument of self-defence; see Identical letters dated 29 July 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (30 July 2015) UN Docs A/69/996–S/2015/574; Identical letters dated 18 January 2016 from the Chargé d’affaires a.i. of the Permanent Mission of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (22 January 2016) UN Doc S/2016/45.

65  Identical letters dated 17 September 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (21 September 2015) UN Doc S/2015/719.

66  Identical letters dated 21 September 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (22 September 2015) UN Docs A/70/385–S/2015/727.

67  Identical letters dated 9 November 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (16 November 2015) UN Doc S/2015/851; Identical letters dated 7 December 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (8 December 2015) UN Doc S/2015/933; Identical letters dated 29 December 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (4 January 2016) UN Doc A/70/673-S/2015/1048; Identical letters dated 22 December 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (7 January 2016) UN Docs A/70/654-S/2015/1014; UN Doc S/PV.7527 (n 38) at 16.

68  UN Doc S/PV.7271 (n 9) at 19. See also ‘Russia Says Air Strikes in Syria Would Be Act of Aggression without UN Vote’ Reuters (11 September 2014) quoted in Tom Ruys and Nele Verlinden, ‘Digest of State Practice (1 July–1 December 2014)’ (2014) 1 Journal on the Use of Force and International Law 135.

69  UN Doc S/PV.7527 (n 38) at 16. See also International Business Times (25 September 2014) <http://www.ibtimes.com/venezuelas-nicolas-maduro-calls-re-founding-un-slams-us-led-airstrikes-iraq-syria-1694699>.

70  UN Doc S/PV.7527 (n 38) at 50.

71  ‘Cuba Advocates Political Solution to Crisis in Syria’ Ahora <http://www.ahora.cu/en/sections/world/1931-cuba-advocates-political-solution-to-crisis-in-syria>.

72  Statement dated 23 September 2014 available at Ministerio de Relaciones Exteriores y Movilidad Humana ‘Ecuador rechaza ofensiva estadounidense en territorio sirio’ <http://www.cancilleria.gob.ec/ecuador-rechaza-ofensiva-estadounidense-en-territorio-sirio/>.

73  See Lindsay Morris, ‘Arab backing for U.S.-led airstrikes in Syria widens front against Islamic State’ The Washington Post (Washington DC, 23 September 2014) <https://www.washingtonpost.com/world/arab-backing-to-us-led-airstrikes-in-syria-widens-front-against-islamic-state/2014/09/23/85664a44-430c-11e4-b437-1a7368204804_story.html>; ‘Syria Air Strikes: Iran “Says US Attacks on Isis Are Illegal” ’ The Independent (London, 23 September 2014) <http://www.independent.co.uk/news/world/middle-east/syria-air-strikes-iran-says-us-attacks-on-isis-are-illegal-9751245.html>; see also UN Doc S/PV.7271 (n 9) 36.

74  UN Doc S/PV.7527 (n 38) 77.

75  Paulina Starski, ‘Right of Self-defense, Attribution and the Non-State Actor – Birth of the “Unable or Unwilling” Standard?’ (2015) 75 Zaörv 34 (citing the Buenos Aires Herald).

76  UNSC Verbatim Record (24 April 2015) UN Doc S/PV.7433, 19; see also UN Doc S/PV.7271 (n 9) at 20; UN Doc S/PV.7527 (n 38) at 6. See also Letter dated 8 July 2016 from the representatives of China and the Russian Federation to the United Nations addressed to the Secretary-General (12 July 2016) UN Doc S/2016/600.

77  UN Doc S/PV.7527 (n 38) 48–49.

78  ibid 53.

79  ibid 57.

80  ibid 65.

81  ibid 18.

82  ibid 80.

83  UN Doc S/PV.7272 (n 9) 7.

84  UN Doc S/PV.7565 (n 44) 8.

85  UNSC Res 2249 (2015) (n 26) [5].

86  Statement by the President of the Security Council (19 September 2014) UN Doc S/PRST/2014/20.

87  UNSC Res 2254 (2015) (18 December 2015) UN Doc S/RES/2254, at [8].

88  By contrast with certain previous resolutions such as UNSC Res 1368 (2001); Carlos Espaliu Berdud, ‘The EU Response to the Paris Terrorist Attacks and the Reshaping of the Right of Self-Defence in International Law’ (2016) Spanish Yearbook of International Law 199–200; Bannelier-Christakis (n 54) 221–22; Nabil Hajjami, ‘De la légalité de l’engagement militaire de la France en Syrie’ (2017) 1 Revue du droit public 174; contra, contending that the Security Council has supported a right to self-defence, Michael Wood, ‘The Use of Force in 2015 with Particular Reference to Syria’ (2016) Hebrew University of Jerusalem Legal Studies Research Paper Series.

89  See the references above. Contra: Michael P Scharf, ‘How the War Against ISIS Changed International Law’ (2016) 48 Case Western Reserve Journal of International Law 51.

90  Statement by the President of the Security Council (19 September 2014) S/2014/20; UNSC Res 2233 (2015) (29 July 2015) UN Doc S/RES/2233; UNSC Res 2253 (2015) (17 December 2015) UN Doc S/RES/2253.

91  Statement by the President of the Security Council (24 April 2015) S/2015/10; Statement by the President of the Security Council (17 August 2015) S/2015/15; UNSC Res 2258 (2015) (22 December 2015) UN Doc S/RES/2258; UNSC Res 2268 (2016) (22 February 2016) UN Doc S/RES/2268; UNSC Res 2328 (2016) (19 December 2016) UN Doc S/RES/2328; UNSC Res 2332 (2016) (21 December 2016) UN Doc S/RES/2332; UNSC Res 2336 (2016) (31 December 2016) UN Doc S/RES/2336; see also ‘Situation of human rights in the Syrian Arab Republic’ UNGA Res 69/189 (18 December 2014) UN Doc A/RES/68/189.

92  UNSC Res 2178 (24 September 2014) S/RES/2178 (2014), at [18]; see also UNSC Res 2195 (19 December 2014) UN Doc S/RES/2195 (2014); UNSC Res 2253 (n 90).

94  See, eg, Corten, ‘The “Unwilling or Unable” Test: Has it Been, and Could it be, Accepted?’ (n 1); Corten, ‘L’argumentation des Etats européens pour justifier une intervention militaire contre l’“Etat islamique” en Syrie: vers une reconfiguration de la notion de légitime défense?’ (n 1).

95  Military and Paramilitary Activities in and against Nicaragua (Nicaragua v USA) (Judgment) [1986] ICJ Rep at 126, [246].

96  Yearbook of the ILC, vol II (Part Two) (1979), 112.

97  Karine Bannelier-Christakis, ‘Military Interventions against ISIL in Iraq, Syria and Libya, and the Legal Basis of Consent’ (2016) 29 Leiden Journal of International Law 760ff.

98  Stefan Talmon, ‘Recognition of Opposition Groups as the Legitimate Representative of a People’ (2013) 12 Chinese Journal of International Law 219.

99  Bannelier-Christakis (n 97) 762.

100  See section II and Bannelier-Christakis (n 97) 762–63.

101  Louise Doswald-Beck, ‘The Legal Validity of Military Intervention by Invitation of the Government’ (1985) 56 British Yearbook of International Law 189–252; Olivier Corten, The Law Against War: The Prohibition on the Use of Force in Contemporary International Law (Hart 2010), Chapter 5; Theodore Christakis and Karine Bannelier, ‘Volenti non fit injuria? Les effets du consentement à l’intervention militaire’ (2004) 50 Annuaire français de droit international 102–37.

102  ‘The Principle of Non-Intervention in Civil Wars’, Institut de droit international, Wiesbaden Session, 1975.

103  Christakis and Bannelier (n 101)118–20.

104  Antonio Coco and Jean Baptiste Maillart, ‘The Conflict with Islamic State: A Critical Review of International Legal Issues’ in Annyssa Bellal (ed), The War Report: Armed Conflicts in 2014 (OUP 2015) 397; Tom Ruys and Luca Ferro (n 18).

105  See Chapter 49, ‘The Iraq War—2003’ by Marc Weller and Chapter 61, ‘The Intervention of France and African Countries in Mali—2013’ by Karine Bannelier and Theodore Christakis in this volume.

106  Karine Bannelier and Theodore Christakis, ‘Under the UN Security Council’s Watchful Eyes: Military Intervention by Invitation in the Malian Conflict’ (2013) 26 Leiden Journal of International Law 855–74.

107  UNSC Res 2249 (2015) (n 26).

108  Nabil Hajjami, ‘Que signifie l’expression ‘prendre toutes les mesures nécessaires’ dans la pratique du Conseil de sécurité des Nations Unies?’ (2013) 47 Revue belge de droit international 232–56.

109  See Peter Hilpold, ‘The Fight Against Terrorism and SC Resolution 2249 (2015): Towards a More Hobbesian or a More Kantian International Society?’ (2015) 55 Indian Journal of International Law 535–55; Peter Hilpold, ‘The Evolving Right of Counter-Terrorism: An Analysis of SC Resolution 2249 (2015) in View of Some Basic Contributions in International Law literature’ (2016) 24 Questions of International Law 15–34.

110  Scharf (n 89) 51; Hajjami (n 88) 169–73; Wood (n 88); Jean-Christophe Martin, ‘Les frappes de la France contre l’EIIL en Syrie, à la lumière de la résolution 2249 (2015) du Conseil de sécurité’ (2016) 24 Questions of International Law 11–14.

111  Laurie O’ Connor, ‘Legality of the Use of Force in Syria Against Islamic State and the Khorasan Group’ (2016) 3 Journal on the Use of Force and International Law 7.

112  UN Doc S/PV.7565 (n 44) 5.

113  ibid.

114  ibid 9.

115  Corten (n 101) 312ff.

116  Letter dated 3 December 2015 from the Permanent Representative of the United Kingdom of Great Britain and Northern Ireland to the United Nations addressed to the President of the Security Council (3 December 2015) UN Doc S/2015/928; Letter dated 10 December 2015 from the Chargé d’affaires a.i. of the Permanent Mission of Germany to the United Nations addressed to the President of the Security Council (10 December 2015) UN Doc S/2015/946; Letter dated 11 January 2016 from the Permanent Representative of Denmark to the United Nations addressed to the President of the Security Council (13 January 2016) UN Doc S/2016/34; Letter dated 10 February 2016 from the Chargé d’affaires a.i. of the Permanent Mission of the Netherlands to the United Nations addressed to the President of the Security Council (10 February 2016) UN Doc S/2016/132; Letter dated 3 June 2016 from the Permanent Representative of Norway to the United Nations addressed to the President of the Security Council (3 June 2016) UN Doc S/2016/513; Letter dated 7 June 2016 from the Permanent Representative of Belgium to the United Nations addressed to the President of the Security Council (9 June 2016) UN Doc S/2016/523.

117  Bannelier-Christakis (n 54), 222–23.

118  Ashley Deeks, ‘ “Unwilling or Unable”: Toward a Normative Framework for Extraterritorial Self-Defense’ (2012) Virginia Journal of International Law 487–88; Theresa Reinold, ‘State Weakness, Irregular Warfare, and the Right to Self-Defence Post-9/11’ (2011) American Journal of International Law 244–86. These two authors seem to consider that the ‘unwillingness’ criteria would oblige the state invoking self-defence to try to obtain the consent of the territorial state first, a step the United States have refused to follow, as mentioned above, see Corten, ‘The “Unwilling or Unable” Test: Has it Been, and Could it be, Accepted?’ (n 1).

119  Emphasis added.

120  Military and Paramilitary Activities in and against Nicaragua (n 95) 98–101, [187]–[190]; Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory (Advisory Opinion) [2004] ICJ Rep 136, at 171, [87]; Armed Activities on the Territory of the Congo (Democratic Republic of Congo v Uganda) (Judgment) [2005] ICJ Rep at 226, [162]; see also Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep 226, at 264, [102].

121  See Starski (n 75); Corten, ‘The “Unwilling or Unable” Test: Has it Been, and Could it be, Accepted?’ (n 1); Flasch (n 10) 16ff; O’Connor (n 111) 19.

122  See Chapter 48, ‘The Intervention in Afghanistan—2001’ by Michael Byers and Chapter 51, ‘The Israeli Intervention in Lebanon—2006’ by Christian J Tams and Wenke Brückner both in this volume.

123  See the references above n 21.

124  Christian Henderson, ‘The Use of Force and Islamic State’ (2014) 1 Journal on the Use of Force and International Law 215–17.

125  Emphasis added; Armed Activities on the Territory of the Congo (n 121) 262, [276].

126  ibid 269, [303]. Emphasis added.

127  See, eg, Institut de droit international, Resolution on Self-defence (Santiago Session, 27 October 2007) [5] and ‘Report of the Independent International Fact-Finding Mission on the Conflict in Georgia’, vol II (September 2009), 242 and 245.

128  Military and Paramilitary Activities in and against Nicaragua (n 95) 126–27, [247].

129  Corten (n 101) 466–70.

130  Review Conference of the Rome Statute of the ICC, Kampala, 31-May-11 June 2010, Res RC/6 of 11 June 2010, Annex I, Amendments to the Rome Statute of the ICC (Article 8bis); see Espaliu Berdud (n 88) 201–02.

131  Latty (n 54) 21–24; Hajjami (n 88) 161.

132  Deeks (n 118) 520.

133  Corten, ‘The “Unwilling or Unable” Theory: Has it Been, and Could it Be, Accepted?’ (n 1).

134  Coco and Maillart (n 104) 403.

135  UNGA Res 2625 (XXV) (24 October 1970) UN Doc A/RES/2625.

136  Definition of aggression, UNGA Res 3314 (XXIX) (14 December 1974) UN Doc A/RES/3314 (XXIX), Annex, Article 3(a) and (b).

137  See Nicholas Tsagourias, ‘Self-Defence against Non-state Actors: The Interaction between Self-Defence as a Primary Rule and Self-Defence as a Secondary Rule’ (2016) 29 Leiden Journal of International Law, even if this author proposes another interpretation of self-defence based on secondary rules of international responsibility.

138  See, eg, Identical letters dated 12 January 2017 from the Chargé d’affaires a.i. of the Permanent Mission of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (16 January 2017) UN Doc S/2017/36. On at least one occasion, it seems that the Syrian armed forces have been touched by a US military operation; see Identical letters dated 17 September 2016 from the Chargé d’affaires a.i. of the Permanent Mission of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (19 September 2016) UN Doc S/2016/790.

139  See, eg, Identical letters dated 27 December 2015 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (30 December 2015) UN Docs A/70/671 and S/2015/1043; Identical letters dated 11 January 2016 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (12 January 2016) UN Doc S/2016/31; Identical letters dated 29 September 2016 from the Permanent Representative of the Syrian Arab Republic addressed to the Secretary-General and the President of the Security Council (30 September 2016) UN Doc S/2016/820; Identical letters dated 11 October 2016 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (12 October 2016) UN Doc S/2016/858; Identical letters dated 26 October 2016 from the Permanent Representative of the Syrian Arab Republic to the United Nations addressed to the Secretary-General and the President of the Security Council (28 October 2016) UN Doc S/2016/900.

140  Hajjami (n 88) 163–64.

141  See Agatha Verdebout, ‘The Contemporary Discourse on the Use of Force in the Nineteenth Century: A Diachronic and Critical Analysis’ (2014) 1 Journal on the Use of Force and International Law 223–46.

142  See, eg, Michael N Schmitt, ‘Counter-Terrorism and the Use of Force in International Law’ (2002) 5 The Marshall Center Papers 22–23; Daniel Bethlehem, ‘Self-Defense Against an Imminent or Actual Armed Attack by Nonstate Actors’ (2012) American Journal of International Law 773; Christopher Greenwood, ‘Self-Defence’ in Max Planck Encyclopedia of Public International Law vol IX (OUP 2012) 112.

143  See, eg, Kimberley Trapp, ‘Can Non-State Actors Mount an Armed Attack?’ in Marc Weller (ed), The Oxford Handbook of the Use of Force in International Law (OUP 2015) 694–95 and ‘Actor-Pluralism, the “Turn to Responsibility” and the Jus Ad Bellum: “Unwilling or Unable” in Context’ (2015) 2 Journal on the Use of Force and International Law 199–222.

144  See, eg, Pierre Klein, ‘Le droit international à l’épreuve du terrorisme’ Collected Courses of the Hague Academy of International Law vol 321 (Brill Nijhoff 2007) 370ff.

145  Corten, The “Unwilling or Unable” Test: Has it Been, and Could it be, Accepted?’ (n 1).

146  Olivier Corten, ‘Necessity’ in Marc Weller (ed), The Oxford Handbook of the Use of Force in International Law (OUP 2015) 861–78.

147  Armed Activities (n 121) 223–24, [148].

148  See Ruys and Ferro (n 104).

149  Corten (n 101) 170.

150  An expression deduced from the Webster doctrine cited in John Bassett Moore, Digest of International Law (Washington Press 1906) 412.

151  Oil Platforms (Islamic Republic of Iran v United States of America) (Judgment) [2003] ICJ Rep 196, [73].

152  Nicaragua case (96) 120, [232].

153  Olivier Corten, ‘L’argumentation des Etats européens pour justifier une intervention militaire contre l’“Etat islamique” en Syrie: vers une reconfiguration de la notion de légitime défense?’ 49 (2016) Revue belge de droit international 60.

154  References above (n 30–32). The French position has been particularly equivocal in this regard; see Hajjami (n 88) 158–59.

155  Theodore Christakis, ‘Existe-t-il un droit de légitime défense en cas de simple “menace”? Une réponse au “groupe de personnalités de haut niveau” de l’ONU’ in SFDI, Les métamorphoses de la sécurité collective (Pedone 2005); Corten (n 101) 406–43. In 2003, in the context of the Iraqi War, more than 250 international lawyers signed a text according to which ‘Self defence presupposes the existence of a prior armed attack; consequently, “preventive self defence” is not admissible under international law in (2003) 36 Revue belge de droit international, 266.

156  Yoram Dinstein, War, Aggression and Self-Defence (5th edn, CUP 2011) 201–07; see also Tom Ruys, ‘Armed Attack’ and Article 51 of the UN Charter (CUP 2010) 346ff.

157  See, eg, Ashley Deeks, ‘Taming the Doctrine of Pre-Emption’ in Marc Weller (ed), The Handbook of the Use of Force in International Law (OUP 2015) 662ff.

158  Corten (n 101) 409–11.

159  A more secured world: Our shared responsibility, Report of the Secretary-General’s High-level Panel on Threats, Challenges and Change, United Nations (2004) UN Doc A/59/565, [188]–[189] and In larger freedom: towards development, security and human rights for all (24 March 2005) UN Doc A/59/2005, 33, [124].

160  Comments of the Non-Aligned Movement on the Observations and Recommendations contained in the Report of the High-Level Panel on Threats, Challenges and Change (28 February 2005) UN Docs A/59/565 and A/59/565CORR.1, [23]–[24].

161  2005 World Summit Outcome (24 October 2005) UN Doc A/RES/60/1, [77]–[79].

162  See the condemnations made by the NAM, eg 14th Summit Conference of Heads of State or Government of the NAM (Havana, Cuba, 11–16 September 2006) 2006/Doc.1/Rev.3, [20.2]; 17th Summit of Heads of State and Government of the Non-Aligned Movement (Venezuela, 16–18 September 2016), [26.5].

163  Contra: Scharf (n 89) 1–54.

164  See Bannelier-Christakis (n 100) 763–66.

165  Bannelier and Christakis (n 106). See also Chapter 61 dedicated to Mali in this volume.

166  Ruys and Ferro, ‘Weathering the Storm: Legality and Legal Implications of the Saudi-Led Military Intervention in Yemen’ (2016) 65 International Comparative Law Quarterly 61–98; Philippe Fabri, ‘La licéité de l’intervention internationale menée par l’Arabie saoudite au Yémen au regard des principes de l’interdiction du recours à la force et de non-intervention dans les guerres civiles’ 49 (2016) Revue belge de droit international 69–102. See also Chapter 65 dedicated to Yemen in this volume.

167  Olivier Corten, ‘La rébellion et le droit international. Le principe de neutralité en tension’ Collected Courses of the Hague Academy of International Law vol 374 (Brill Nijhoff 2014) 53–312.

168  Paulina Straski, ‘Silence Within the Process of Normative Change and Evolution of the Prohibition on the Use of Force Normative Volability and Legislative Responsibility’ (2017) 4 Journal on the Use of Force and International Law.

169  Final Communiqué of the 9th extraordinary session of the Islamic Conference of the Ministries of Foreign Affairs (Doha, Qatar, 10 October 2001).

170  NAM, Final Document of the Fourteenth Conference of Heads of State or Government of Non-Aligned Countries (Havana, Cuba, 11–16 September 2006) available in ‘Letter dated 2006/09/19 from the Permanent Representative of Cuba to the United Nations addressed to the Secretary-General’ (29 September 2006) UN Docs A/61/472–S/2006/780, Annex 1 [142]–[143]. See Olivier Corten and Agatha Verdebout, ‘Les interventions militaires récentes en territoire étranger: vers une remise en cause du jus contra bellum?’ (2014) Annuaire français de droit international 144–47.

171  17th Summit of Heads of State and Government of the Non-Aligned Movement (n 162) [25.2]. See also, NAM, XVII Ministrial Conference of the Non-Aligned Movement Final Document (Algiers, Algeria, 26–29 May 2014) available in ‘Letter dated 1 August 2014 the Chargé d’affaires a.i. of the Permanent Mission of the Islamic Republic of Iran to the United Nations addressed to the Secretary-General’ (19 August 2014) UN Docs A/68/966 and S/2014/573, Annex 1 [25.2]; UNSC Verbatim Record (15 February 2016) UN Doc S/PV.7621, 34.

172  Bannelier-Christakis (n 54) 225–26; Tina Korošec and Maruša T Veber, ‘The Right of Self-Defence in International Law: Contemporary Developments in the Context of Fight against Terrorism’ (2016) 76 Zbornik znanstvenih razprav Letnik 41–68.

173  In favour of this thesis, see, eg, Thomas Franck, ‘Terrorism and the Right of Self-Defense’ (2001) 95 American Journal of International Law 840; Sean D Murphy, ‘Terrorism and the Concept of “Armed Attack” in Article 51 of the U.N. Charter’ (2002) 43 Harvard International Law Journal 50; Christian Tams, ‘The Use of Force against Terrorists’ (2009) 20 European Journal of International Law 378ff; Dinstein (n 157) 227–30; Bethlehem (n 143) 774.

174  Reproduced in (2016) 49 Revue belge de droit international 10. Among the signatories, we find international lawyers from various countries, including Georges Abi Saab, Philip Alston, Tony Anghie, Mariano Aznar, Rafâa Ben Achour, Michael Byers, Enzo Cannizaro, Hilary Charlesworth, Luigi Condorelli, Pierre-Marie Dupuy, Christine Gray, James A Green, Christian Henderson, Jörg Kammerhofer, Maurice Kamto, Jan Klabbers, Martti Koskenniemi, Nico Krisch, Auguste Mampuya, Djamchid Momtaz, Gérard Nyiungeko, Mary Ellen O’Connell, Yasuaki Onuma, Anne Orford, Mónica Pinto, Balakrishnan Rajagopal, Marco Sassoli, Dire Tladi, Emmanuelle Tourme-Jouannet.