Self-defence against non-State actors, such as pirates and ships carrying letters of marque with deliberately ambiguous links to sovereign States, was the cardinal issue that framed and propelled the rise of modern international law. After the adoption of the UN Charter, the concept of self-defence has been sharpened to mean first of all the situation that one State defends itself against an ongoing armed attack by another State. However, the concept has remained controversial at the margins.
This book is about the major controversy related to the transnational activities of armed non-State groups.Footnote 1 Terrorist organisations have become a major security concern for States in all parts of the world. Terrorism has been qualified by the Security Council as ‘one of the most serious threats to international peace and security’.Footnote 2 Recurring strikes by armed terror groups raise the questions of whether and when such resort to armed force by non-State actors triggers the right to self-defence under international law.Footnote 3
The international lawfulness of military reactions against physical violence exercised by non-State actors but unequivocally imputable to another State is fairly easy to assess. In terms of the International Court of Justice’s Nicaragua judgment, attacks by non-State armed groups are attributable to a State when that State has sent them or when the latter is ‘substantially involved’ (referring to Article 3 lit. g of the General Assembly Definition on Aggression (3314) of 1974).Footnote 4 An alternative criterion figuring prominently in the international legal debates lies in the standard of ‘effective control’, which is the general standard for attribution in the international rules on State responsibility.Footnote 5 Where imputation is possible under these standards, the attacked State may take necessary and proportionate action against the State from whose territory the non-State actors operate, because the acts of the non-State actors are – from a legal perspective – those of the State.
I. The Controversy Around Self-Defence against Non-State Actors
The controversial constellation is defensive action taken against an – as Dire Tladi calls it in this volume – ‘innocent State’,Footnote 6 that is a State to which the military operation of an armed group is not imputable under the acknowledged principles. This scenario raises the questions of whether a lower degree of State involvement is or should be sufficient to allow for self-defence affecting that ‘innocent’ State, and whether imputation to the territorial State matters at all.
It is by no means a new phenomenon that States use military force against non-State actors which operate independently from or at least not under the actual control of another State. In this book, Christian Tams reminds us of various instances since the 1940s. He pleads for acknowledging the nuances in the law which was – so he claims – not as straightforwardly State-oriented as standard narratives would have us believe.Footnote 7 However, while States did defend themselves against non-State actors by military means, these hardly triggered any international legal debate. Legal writings in the early days of the Charter did not take up the issue at length, but largely presupposed a State-oriented reading of the rules on self-defence.Footnote 8 While in the following decades a few especially affected States such as Israel took a clear position on the issue,Footnote 9 the underlying general question was not made a direct subject of controversy.
This changed significantly with the terrorist attacks of 9/11 in 2001 and with the subsequent military interventions. These events are often seen as constituting a ‘true turning point’ in the debate on the international law of self-defence.Footnote 10 Since the military intervention of the United States and its allies in Afghanistan in 2001, self-defence – and especially against non-State actors – figures as a, if not the, controversial issue of international peace and security law.Footnote 11 The primary target of the United States was the terrorist organisation Al-Qaeda. The US army intervened in Afghanistan, which the US accused of allowing ‘the parts of Afghanistan that it controls to be used by this organization as a base of operation’.Footnote 12 As Afghanistan did not have ‘effective control’ over Al-Qaeda, the traditional criteria of imputation would not have allowed defensive action against its territory. Many observers interpret the US intervention and the international reactions to that intervention as triggers of a sudden shift in the law, partly described as a case of ‘instant custom’.Footnote 13
Those assuming such a shift in the law mainly point to Security Council resolutions 1368 and 1373 of September 2001.Footnote 14 These resolutions mention the inherent right of self-defence in their preambles before condemning the terrorist attacks of 9/11. While self-defence does not need a licence by the Security Council, and although the Council cannot unilaterally change the law of the Charter, its explicit classification of a terrorist threat as an armed attack would have contributed to the formation of a novel interpretation and opinio iuris in this direction.Footnote 15 Many observers interpret the resolutions’ language as an endorsement by the Security Council of a right to self-defence against the non-State group Al-Qaeda.Footnote 16 Along the same line, the international support for the US, in combination with the absence of a condemnation of the military intervention in Afghanistan, is interpreted as acquiescence, or at least as a toleration, of a broader legal rule on self-defence.Footnote 17
The question, however, has remained controversial. Critics of the extended notion of self-defence insist that the Security resolutions of 2001 only mention the right to self-defence without passing a judgment on its lawful use in the concrete case of the strikes against Al-Qaeda on Afghan territory.Footnote 18 Besides, the international reactions to the invasion in Afghanistan, especially the laconism or muteness of many States, have been interpreted in different ways. The opponents of the broader reading of self-defence explain the silence of many States as a politically motivated restraint that was not intended to have an influence on the law and thus does not express any opinio iuris.Footnote 19
The case-law of the International Court of Justice has not settled the issue. While the Advisory Opinion on the Israeli Wall of 2004 is mostly read as leaning towards a State-oriented reading of self-defence,Footnote 20 the ICJ judgment in Congo v. Uganda of 2005 gave room for much debate.Footnote 21 For many readers, this judgment signalled that the ICJ was open for accepting self-defence against non-State actors.Footnote 22
International legal scholars and practitioners have developed a number of proposals for dealing with self-defence against non-State actors: the Chatham House Principles,Footnote 23 the Leiden Policy Recommendations,Footnote 24 and the Bethlehem Principles.Footnote 25 These sets of principles and recommendations purport to describe actual State practice and the current state of the law and (partly) make de lege ferenda proposals.Footnote 26 While they significantly diverge in their details, these proposals all assume that self-defence against non-State actors on the territory of a non-consenting State is lawful (or in the process of becoming the law, or should be allowed) in situations where the territorial State is either unwilling or unable to prevent attacks by non-State actors emanating from its territory.Footnote 27
Many scholarly writings of the post-9/11 era, however, have remained more cautious. A general undertone of the debate has been an acknowledgement of a certain tendency towards a broader reading of self-defence, while formulations have often remained far from unequivocally postulating such an understanding. In that sense, commentators have stated, for example, that an extensive interpretation of self-defence ‘appears to be gaining ground’,Footnote 28 and that a ‘trend … clearly [points] towards the establishment of an even further-reaching responsibility of the host state based on the mere toleration or harbouring of terrorists.’Footnote 29 Christian Tams held in an earlier article that ‘the international community today is much less likely to deny’ a State’s invocation of self-defence against attacks not imputable to a State.Footnote 30 Claus Kress found that an ‘alleged right of self-defence in case of a non-State armed attack now occupies a place within the “light grey” area of the international law on the use of force’.Footnote 31 Thus, even positions generally agreeing that the solely State-centred reading of self-defence had come under immense pressure were hesitant to outrightly assume that a clear shift in the law had already taken place.
II. Revival of the Debate since 2014
The debate about whether and under what conditions self-defence is lawful against (certain types of) non-State attacks has received renewed attention since 2014 due to the interventions of numerous States in the armed conflict in Syria. In this context, a number of States – notably the United States, Turkey, the United Kingdom, and France – have claimed to act in individual self-defence against Islamist terrorist groups, above all against the group Islamic State of Iraq and Syria (ISIS).Footnote 32 Some States alternatively or additionally relied on the collective self-defence of Iraq,Footnote 33 and thus presupposed that Iraq was suffering an armed attack in the sense of Article 51 of the UN Charter.
The Security Council has assumed an equivocal position on interventions in Syria. In its Resolution 2249, it ‘calls upon’ member States to participate in the fight against ISIS, but did not itself authorise an intervention under Chapter VII of the UN Charter.Footnote 34 Furthermore, the Council did not even mention self-defence (not even in the preamble) – unlike in its Resolution 1368 after 9/11. It limited its ‘call’ to measures ‘in compliance with international law’.Footnote 35 This reference to ‘international law’ can be read in various ways. It is at first sight a reminder that any reaction must be lawful. It might also be a veiled reference to the law of self-defence, avoiding an explicit mentioning, so as to escape a repetition of the post-9/11 controversy regarding whether the Security Council had endorsed the American claim of self-defence or not. The Security Council thereby left the controversial question of self-defence against non-State actors to the interpretation of the States. Unsurprisingly, the (probably deliberately) cryptic resolution has been interpreted both ways, as remaining within the boundaries of the established State-centred law, on the one hand,Footnote 36 and as embracing a broadened understanding of self-defence, on the other.Footnote 37
Among the intervening States, the conditions of lawful self-defence are far from agreed. Rather, the participating States have invoked diverse rationales for their interventions, ranging from the ‘unwilling or unable’ standard (proclaimed by the United States, Australia, Canada and Turkey)Footnote 38 to the criterion of effective territorial control (emphasised by Belgium and Germany).Footnote 39 In the course of the conflict in Syria, the extended understanding of self-defence has not only been invoked against ISIS. Turkey has also claimed to act in self-defence against the Kurdish militia YPG. In its operation ‘Olive Branch’, commenced in January 2018, Turkey claimed the right to defend itself against the ‘threat from the Syria-based terrorist organizations, among which Deash and the PKK/KCK Syria affiliate, PYD/YPG, are at the top of the list’.Footnote 40
Some observers have interpreted recent State activity in Syria as giving the ‘final push’ to a change in the law.Footnote 41 In view of significant State practice supporting a broader understanding of self-defence, and in view of widespread scholarly endorsement of this broad reading,Footnote 42 it partly seemed as if, in the words of van Steenberghe, ‘the orthodoxy on the law on the use of force has dramatically switched from a restrictivist to an expansionist perspective.’Footnote 43 However, pronounced scepticism towards the broader reading,Footnote 44 notably against the ‘unwilling or unable’ formula,Footnote 45 persists. An important academic action was the ‘Plea against the Abusive Invocation of Self-Defence as a Response to Terrorism’, initiated by Olivier Corten in 2016, which found the support of more than 240 international lawyers and professors from a wide range of countries.Footnote 46 The plea explicitly rejects the ‘unable’ part of the ‘unwilling or unable’ doctrineFootnote 47 and perceives ‘a serious risk of self-defence becoming an alibi, used systematically to justify the unilateral launching of military operations around the world’.Footnote 48 Further commentators criticise the ‘unable or unwilling’ standard from the perspective of weaker States, and in particular the Global South, as ‘ignoring the unequal international environment in which the doctrine operates’.Footnote 49 This doctrine will not apply in powerful States, but it is a legal framework for what Jochen von Bernstorff has called the ‘semi-periphery’-States ‘that do not belong to the inner circle or are not powerful enough to resist the application of the regime’.Footnote 50 In this vein, the ‘unwilling or unable’ standard has been especially criticised from a post-colonial perspective as a vehicle for ‘reintroduc[ing] a hierarchy of States in the operation of jus ad bellum’ – a hierarchy that echoes ‘the infamous nineteenth-century distinction between civilized, semi-civilized and uncivilized states’.Footnote 51
III. Three Perspectives in a Trialogue
Against this background, this Trialogue raises a seemingly simple yet complex set of interrelated questions. Does international law as it stands allow for self-defence against non-State actors on the territory of a non-consenting State? Has an evolution of the law occurred in this regard, and, if yes, when and how? Assuming there has been legal evolution, what does this mean in terms of legal policy? What are the repercussions for the entire regime of the ius contra bellum, and for the international legal order at large?
The first two questions are primarily doctrinal, about the current state of law and the modes of legal change. Answering them requires an engagement with the doctrines on the sources of international law and hence with recent State practice. The aim is to identify whether and to what extent the numerous proposals and normative claims about self-defence that have been brought up in practice and theory have actually solidified into hard international rules and generally accepted interpretations.
As explained in the Introduction to the series, it is the characteristic feature of a Trialogue to approach the research questions from three perspectives which differ in terms of regional background, technical method, and worldview of the discussants.Footnote 52 Dire Tladi was invited to the Trialogue for his unique experience as a South African scholar and Professor of International Law at the University of Pretoria who has, at the same time, significant experience in the practice of international law. In addition to his academic appointments and scholarly work, he has served as the Principal State Law Adviser for International Law for the South African Department of International Relations and Cooperation and as legal adviser to the South African Permanent Mission to the United Nations. Moreover, he is a member of the International Law Commission and its Special Rapporteur on Peremptory Norms of General International Law (Jus Cogens). With such a background, Tladi is in a position to clearly assess the consequences of an extended reading of self-defence for States that are potentially not powerful enough to resist outside intervention in the fight against terrorism.
In his contribution to this Trialogue, Tladi espouses a ‘positivist approach to the identification of the law’,Footnote 53 aiming for the ‘objectively correct interpretation’ of the rules of international law on self-defence.Footnote 54 He offers an account of self-defence whose core is the embeddedness of this legal institution within a system of collective security. Tladi sets out the principles of the prohibition on the use of force and of collective security. Then, based on arguments of context and purpose, he advocates what has long been the largely uncontroversial interpretation, namely a State-centred reading of the rules on self-defence which requires attribution of the strikes by the non-State actors to a State. He accepts the possibility that State practice, whether as a constituent element of customary international law or as subsequent interpretation of article 51, can affect the State-centred interpretation of the law on self-defence. Having assessed the practice that is often put forward in support of a shift, including the interventions in Afghanistan and Syria, he concludes that the established notion of self-defence as requiring an armed attack from a State is still good law and has not been changed.
The second co-author of the Trialogue is Christian Tams, Professor of International Law at the University of Glasgow. Tams received his legal education in both Germany and the United Kingdom, and was invited to the Trialogue as someone who has been exposed to both the doctrinal rigour of the German legal system as well as to the case- and practice-oriented perspective commonly found in the Anglo-Saxon approach to international law.
Tams frames the issue of the legality of self-defence against non-State actors as a pure question of treaty interpretation, namely of the interpretation of the term ‘armed attack’ contained in Article 51 of the UN Charter. Tams essentially follows the structure of Articles 31 and 32 VCLT as a guideline to interpretation and provides a rich discussion of the wording, context, object and purpose as well as the preparatory work. His main focus rests on a discussion of practice since 1945. He embraces what he has described elsewhere as ‘the uncertainty of old’, arguing that self-defence against non-State actors has always been present in international practice since the foundation of the UN.Footnote 55 Tams rejects what he calls the ‘popular narrative’. According to that narrative, the ‘law of self-defence was “sufficiently clear”’ until the 1990s or even until 2001, when (potentially) a sudden shift in practice and law was triggered by the events of 9/11.Footnote 56 Tams thus departs from a different starting point than Tladi for his legal assessment. In Tams’ view, we should not presume a basically unequivocal old State-centred law whose changes we ought to discuss in light of recent State practice based on new legal justifications. Rather, State practice, e.g. in Afghanistan and Syria, only carries on and has thereby intensified the legal justifications that were present before. The law was – so Tams argues – uncertain in the first place. Therefore, importantly, the standards for the operation of ‘a change in the law’ are significantly different from, if not actually lower than for, constellations in which an old rule was clear and strong. In discussing recent events as ‘subsequent practice’ (in the sense of Article 31(3)(b) VCLT) against the backdrop of ‘the uncertainty of old’, Tams arrives at the conclusion that international law in principle does allow for self-defence actions to be taken against non-State actors, independently of any attribution to a State.
The third co-author of the Trialogue is Mary Ellen O’Connell, Professor of International Law at the University of Notre Dame in the United States. She received her legal education in the United Kingdom and the US, and has specialised in the law of the use of force and has, inter alia, chaired the Use of Force Committee of the International Law Association and was a professional military educator for the US Department of Defense in Germany for several years. We invited her to the Trialogue for her normative approach to international law, at the core of which is a strong sceptical attitude toward the utility and morality of using military force.
Mary Ellen O’Connell’s reading of the UN Charter is underpinned by natural law theory that she regards as the basis of the prohibition on the use of force. She generally shares Dire Tladi’s argumentative direction by rejecting an extended reading of self-defence. She identifies and discusses three ‘pernicious doctrines of expansive self-defence’,Footnote 57 namely the assertion of a right to defend oneself against imminent attacks, the treatment of terrorist crimes as armed attacks, and the assertion of the ‘unwilling or unable’ doctrine to satisfy or substitute for the requirements of attribution or consent. With Dire Tladi, and in contrast to Christian Tams, she shares the assumption of a clear State-oriented character of the ius contra bellum. In contrast to Tladi, however, her main argument does not rest on an interpretation of recent State practice. Rather, central to O’Connell’s argument is what she defines as the natural law/ius cogens character of the prohibition on the use of force and its exceptions. In her understanding, the ius cogens character restricts the possibility of derogation. This means that the prohibition may not be reduced or diluted by means of subsequent practice; and this guarantees that the law is not affected by contrary practice.
We hope that the readers of the three contributions will, not least through the numerous cross-references, be able to trace the trialogical exchange of arguments and considerations, and sense not only the tensions and undercurrents but also identify the concessions and winning arguments, and ultimately be empowered to form a better informed view on the legality, the politics, and the morality of self-defence against non-State actors.
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