¹ See art 51 UN Charter and Case Concerning Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Judgment (Merits) [1986] ICJ Rep 14, para 176.

² Art 51 UN Charter.

³ Nicaragua (n 1) para 176; Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion [1996] ICJ Rep 226, para 41; Case Concerning Oil Platforms (Islamic Republic of Iran v. United States of America), Judgment (Merits) [2003] ICJ Rep 161, para 76.

⁴ Art 51 UN Charter.

⁵ ibid.

⁶ Nicaragua (n 1) para 34 (confirming that the principle of non-use of force is established in customary law).

⁷ Dinstein, Y, War, Aggression and Self-Defence (CUP 2017) 90CrossRefGoogle Scholar.

⁸ Brownlie, I, International Law and the Use of Force by States (OUP 1963) 362CrossRefGoogle Scholar.

⁹ See Section II.

¹⁰ For an overview of Israel's construction of the wall see Report of the Secretary-General Prepared Pursuant to General Assembly Resolution ES-10/13, UN Doc. A/ES-10/248 (November 24, 2003).

¹¹ UNGA A/ES-10/PV.21 (October 20, 2003).

¹² ibid 5–8 (remarks of the Israeli representative to the UN).

¹³ UNGA Res ES-10/14 (December 8, 2003).

¹⁴ Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion [2004] ICJ Rep 136, para 137.

¹⁵ ibid para 139.

¹⁶ ibid para 35 (Separate Opinion of Judge Higgins).

¹⁷ ‘The State finds itself in a position of self-defence when it is confronted by an armed attack against itself in breach of international law. It is by reason of such a state of affairs that, in a particular case, the State is exonerated from the duty to respect, vis-à-vis the aggressor, the general obligation to refrain from the use of force’; International Law Commission, Eighth Report on State Responsibility by Mr Roberto Ago, Special Rapporteur – The Internationally Wrongful Act of the State, Source of International Responsibility (Part 1), UN Doc A/CN.4/318/Add.5-7 (1980) para 87.

¹⁸ International Law Commission, Second Report on State Responsibility by Mr James Crawford, UN Doc A/CN.4/498 and Add 1-4 (1999) para 298.

¹⁹ ibid.

²⁰ The UN General Assembly has on several occasions commended the ILC's ASR to UN member States; UNGA Res. 56/83 (2001); UNGA Res. 59/35 (2004); UNGA Res. 62/61 (2007); and UNGA Res. 65/19 (2010).

²¹ International Law Commission, Articles on State Responsibility for Internationally Wrongful Acts, with Commentaries (2001) Commentary to art 21, para 1.

²² ibid Commentary to art 21, para 2. On the relationship between self-defence under art 51 UN Charter and art 21 ASR see Tsagourias, N, ‘Self-Defence against Non-State Actors: The Interaction between Self-Defence as a Primary Rule and Self-Defence as a Secondary Rule’ (2016) 29 LJIL 801CrossRefGoogle Scholar.

²³ ‘[Article 51 UN Charter and Article 21 ASR] are, of course, not independent: self-defence's role as a secondary rule is merely incidental to its role as a primary rule. Therefore, to exonerate the breach of other obligations, self-defence must have been lawfully exercised in accordance with the primary law to begin with’; Paddeu, F, ‘Self-Defence as a Circumstance Precluding Wrongfulness: Understanding Article 21 of the Articles on State Responsibility’ (2015) 85 BYBIL 90, 107Google Scholar.

²⁴ ‘Self-defense is the use of force by a person illegally attacked by another. The attack against which the use of force as an act of self-defense is permitted must have been made or must be intended to be made by force’; Kelsen, H, ‘Collective Security and Collective Self-Defense under the Charter of the United Nations’ (1948) 42 AJIL 783, 784CrossRefGoogle Scholar. ‘[Self-defence] is the concrete, subjective, eventual and transitory right of the State to use force in order to repel an attack against its territory and its sovereignty’; Alfaro, RJ, ‘The Rights and Duties of States’ (1959) 97 Recueil des Cours 91, 102–3Google Scholar. ‘The reference to self-defense in Article 51 is a justification for otherwise illegal violence for the simple reason that self-defense has always been a defense in international law for using military force’; GP Fletcher and JD Ohlin, Defending Humanity: When Force Is Justified and Why (OUP 2008) 66. ‘The right of self-defence is an exception to the prohibition of force, so that if the prohibition is limited to military force (direct or indirect as it may be) then the exception must be about the use of military force as well: the whole point of an exception is to exclude the application of the (general) rule from conduct which would otherwise fall within the domain of that (general) rule’; Paddeu (n 23) 110. ‘[L]a letter et l'esprit de l'article 51 de la Charte des Nations Unies indiquent qu'au contraire la légitime défense consiste en une réaction á la force par la force et plus particulièrement en une riposte armée face á une agression armée. L'idée d'une adéquation qualitative entre le fait et la riposte déborde par ailleurs le régime de la Charter et se retrouve en droit coutumier contemporain’; L-A Sicilianos, Les réactions décentralisées à l'illicite (LGDJ 1990) 292, (‘[T]he letter and spirit of Article 51 of the Charter of the United Nations indicate that, on the contrary, self-defence consists of a reaction to force by force and more particularly of an armed response to armed aggression. The idea of equivalence between the fact and the response goes beyond the Charter regime and is found in contemporary customary law' (author's translation)). ‘Article 51, as such, is an exception to the prohibition on the use of force laid down in Article 2(4) of the Charter and thus encompasses only forcible measures’; O'Keefe, R, ‘Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory: A Commentary’ (2004) 37 Revue Belge de Droit International 92, 142Google Scholar (citations omitted). ‘[Article 51 UN Charter] is a limited exception to Article 2(4) allowing self-defense in a situation in which it can be shown by the tangible evidence of an armed attack that a state may respond’; ME O'Connell, The Power and Purpose of International Law (OUP 2008) 165.

²⁵ Scobbie, I, ‘Smoke, Mirrors and Killer Whales: The International Court's Opinion on the Israeli Barrier Wall’ (2004) 5 German Law Journal 1107, 1128-9CrossRefGoogle Scholar (citations omitted). Also defending Judge Higgins's statement, Kritsiotis explains that ‘[t]he right of self-defence was there to justify the application – that is, the threat or the use – of force in international law; it was not there as a default argument for all manner of actions that states may devise or deem necessary to ensure [self-defence]’; D Kritsiotis, ‘A Study of the Scope and Operation of the Rights of Individual and Collective Self-Defence under International Law’ in ND White and C Henderson (eds), Research Handbook on International Conflict and Security Law: Jus ad Bellum, Jus in Bello and Jus post Bellum (Edward Elgar 2013) 173.

²⁶ See eg, DW Bowett, Self-Defence in International Law (MUP 1959) 270 (and, later, Bowett, DW, ‘Economic Coercion and Reprisals by States’ (1972) 13 VaJIntlL 1, 7Google Scholar); Tams, CJ, ‘Light Treatment of a Complex Problem: The Law of Self-Defence in the Wall Case’ (2006) 16 EJIL 975, fn 75Google Scholar; Solomon, S, ‘The Great Oxymoron: Jus in Bello Violations as Legitimate Non-Forcible Measures of Self-Defense: The Post-Disengagement Israeli Measures towards Gaza as a Case Study’ (2010) 9 ChineseJIL 501Google Scholar.

²⁷ Nicaragua (n 1) para 176.

²⁸ Roscini, M, the, ‘On ‘Inherent’ Character of the Right of States to Self-Defence’ (2016) 4 CJICL 634Google Scholar.

²⁹ H Kelsen, Principles of International Law (Rinehart and Co. 1952) 59. ‘In the last resort almost the whole of the duties of states are subordinated to the right of self-preservation’; WE Hall, A Treatise on International Law (Clarendon Press 1884) 244. ‘From the earliest time of the existence of the Law of Nations self-preservation was considered sufficient justification for many acts of a State which violate other States’; L Oppenheim, International Law: A Treatise, Vol. 1 (Peace) (Longmans, Green & Co. 1912) 184.

³⁰ Jennings, RY, ‘The Caroline and McLeod Cases’ (1938) 32 AJIL 82CrossRefGoogle Scholar.

³¹ The Caroline incident in 1837—discussed in detail below—is often seen as subjecting the right of self-defence to the principles of necessity and proportionality.

³² ‘John Forsyth, Secretary of State of the United States, to Powhatan Ellis, United States Chargé d'Affairs at Mexico City, December 10, 1836’ in WR Manning (ed), Diplomatic Correspondence of the United States: Inter-American Affairs 1831–1860 (1937) Vol. 8 (Mexico 1831–1848 (Mid-Year)) 73.

³³ ‘Manuel Eduardo de Gorostiza, Mexican Minister to the United States, to Asbury Dickens, Acting Secretary of State of the United States, October 10, 1836’, ibid 367.

³⁴ ‘Asbury Dickins, Acting Secretary of State of the United States, to Manuel Eduardo de Gorostiza, Mexican Minister to the United States, October 13, 1836’, ibid 67.

³⁵ ‘In this regard the incident that became the classic exposition of the criteria for legally justified self-defence was not perceived as occurring during a war and was thus technically irrelevant to the laws of war’; C Chinkin and MK Kaldor, International Law and New Wars (CUP 2017) 133.

³⁶ ‘Letter from Stevenson to Palmerston (22 May 1838)’ in Manning (n 32) 454.

³⁷ ‘Letter from Webster to Fox (24 April 1841)’, ibid 145.

³⁸ ‘Letter from Ashburton to Webster (28 July 1842)’, ibid 767.

³⁹ Fur Seals Arbitration (1893) 1 Moore Arbitrations 755, 906.

⁴⁰ ibid 839–40.

⁴¹ ibid 938–9.

⁴² ‘It is submitted that the practice of states between 1920 and 1945, and more particularly between 1928 and 1945, provides adequate evidence of a customary rule that the use of force as an instrument of national policy other than under a necessity of self-defence was illegal’; Brownlie (n 8) 110.

⁴³ Tams (n 26) 975, fn 75. See also J Rohlik, ‘Some Remarks on Self-Defense and Intervention: A Reaction to Reading Law and Civil War in the Modern World’ (1976) 6 Georgia Journal International and Comparative Law 395, 415–16 and E Gross, ‘Combatting Terrorism: Does Self-Defense Include the Security Barrier? The Answer Depends on Who You Ask’ (2005) 38 CornellIntlLJ 569, 577.

⁴⁴ AX Fellmeth and M Horwitz, Guide to Latin in International Law (2009) 127 (‘“In the greater is always included the lesser” … meaning that a reference to a composite or more general thing always encompasses a reference to its subdivisions or components’).

⁴⁵ As the ILC concludes, these types of interpretative maxims ‘are, for the most part, principles of logic and good sense valuable only as guides to assist in appreciating the meaning which the parties may have intended to attach to the expressions that they employed in a document’; Reports of the Commission to the General Assembly, Report of the International Law Commission on the Work of its Eighteenth Session, Law of Treaties, UN Doc A/ 6309/Rev.1 (1966) 218.

⁴⁶ Application for Review of Judgment No. 158 of the United Nations Administrative Tribunal [1973] ICJ Rep. 166, para 7 (Dissenting Opinion of Judge de Castro).

⁴⁷ ‘Although collective self-defence is normally discussed as involving the use of force, there is no reason why it should not be limited in certain cases to economic measures. Qui peut le plus, peut le moins’; PJ Kuyper, ‘Community Sanctions against Argentina: Lawfulness under Community and International Law’ in D O'Keefe and HG Schermers (eds), Essays in European Law and Integration (Kluwer 1982) 162.

⁴⁸ UNGA A/ES-10/PV.21 (n 11) 6.

⁴⁹ International courts have frequently used the structure of treaties to inform their interpretation of treaty provisions. See, for example, Acevedo Buendia et al. (Discharged and Retired Employees of the Comptroller) v Peru, Inter-American Court of Human Rights, Judgment (Preliminary Objection, Merits, Reparations and Costs) (July 1, 2009) para 100.

⁵⁰ ‘States simply did not discuss article 51 in relation to the prohibition of force. They only discussed the article in relation to the authority of the Security Council and the permissibility of regional arrangements’; AA Haque, The United Nations Charter at 75: Between Force and Self-Defense – Part Two (24 June 2020) Just Security, <https://www.justsecurity.org/70987/the-united-nations-charter-at-75-between-force-and-self-defense-part-two/>.

⁵¹ Documents of the United Nations Conference on International Organization, San Francisco (1945) Vol. XVII, Documents of the Coordination Committee Including Documents of the Advisory Committee of Jurists, Part I (1954) 287. The Soviet delegate also explained that ‘the only reason for this Article was that it was an exception to the general rule provided in Chapter VII’; ibid. Similarly, the US delegate ‘insisted that [Article 51] was a general exception to the Council machinery and belonged where the powers of the Security Council were stated, in Chapter VII’; ibid 288.

⁵² ‘[T]he criterion of force is an arbitrary one which does not find support in state practice’; Bowett, ‘Economic Coercion and Reprisals by States’ (n 26) 23. Bowett reaffirms this view when he explains that ‘the right of self-defence, though chiefly relevant as an exception to the prohibition of force and as a reaction to a delictual use of force, cannot be and has not been by state practice confined to this context’; ibid 24.

⁵³ UNCIO, Vol. 12, 680.

⁵⁴ Memorandum of Conversation with Senator Tom Connally and Senator Arthur Vandenburg (February 5, 1949), Acheson Papers, <https://perma.cc/K8SM-WM2S>. For the US, the declaration of war is a national decision which, under art 1(8) of the Constitution, requires congressional approval.

⁵⁵ North Atlantic Treaty Organization, ‘Collective Defence and Article 5’, <https://www.nato.int/cps/en/natohq/topics_110496.htm#:~:text=NATO%20invoked%20Article%205%20for,of%20the%20Russia%2DUkraine%20crisis.>

⁵⁶ ibid.

⁵⁷ ‘Article 5 thus merely gives effect to the inherent right of collective self-defence recognized by Article 51 of the Charter’; A Sari, ‘The Mutual Assistance Clauses of the North Atlantic and EU Treaties: The Challenge of Hybrid Threats’ (2019) 10 Harvard National Security Journal 405, 412. See also H Kelsen, ‘Is the North Atlantic Treaty in Conformity with the Charter of the United Nations?’ (1950) 19 Kansas City Law Review 1 and R Buchan and N Tsagourias, Regulating the Use of Force in International Law: Stability and Change (Edward Elgar 2021) 165.

⁵⁸ Art 103 UN Charter also reinforces the idea of compatibility between the UN Charter and the North Atlantic Treaty because it accords primacy to UN obligations over obligations arising under any other international agreement. Thus, it can be assumed that, as UN members, NATO members formulated (and have subsequently interpreted) art 5 of the North Atlantic Treaty compatibly with art 51 UN Charter because any incompatibility between them would in any event have to be resolved in favour of art 51.

⁵⁹ S. Res. 239, 80th Cong., 94 Cong. Rec. 7791 (1948).

⁶⁰ Keesing's (1982) 31532.

⁶¹ UN Doc S/14976 (April 14, 1982) (Belgium, Denmark, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands and the UK).

⁶² Council Regulation (EEC) No. 877/82 in OJ L.102/1 (April 16, 1982). The embargo was extended by Council Regulations (EEC) No. 1176/82 in OJ L.136/1 (May 18, 1982) and No. 8254/82 in OJ L.146/1 (May 25, 1982).

⁶³ Australian Practice in International Law 1981 to 1983 (1983) 10 AustYBIL 573.

⁶⁴ Canadian Practice in International Law during 1982 (1983) 21 CanYBIL 337.

⁶⁵ Keesing's (1982) 31533.

⁶⁶ GATT Doc L/5317 (April 30, 1982).

⁶⁷ Whether economic sanctions breach international law has long divided international lawyers. However, for present purposes what is important is that these States regarded such measures as constituting a prima facie breach of international law and sought to justify them as acts of self-defence.

⁶⁸ Joint Communiqué (EEC, Canada, Australia), Trade Restrictions Affecting Argentina Applied for Non-Economic Reasons, GATT Doc. L/5319/Rev.1 (May 18, 1982) para 1b.

⁶⁹ CJ Tams, Enforcing Obligations Erga Omnes in International Law (CUP 2005) 216.

⁷⁰ GATT Doc C/M/157 (June 22, 1982) 10 (emphasis added).

⁷¹ See OJ 1979, L/298/2 (November 26, 1979; textiles) and OJ 1980, L/275/14 (October 14, 1980: lamb and mutton). These agreements do not contain security exceptions.

⁷² Paddeu (n 23) 110–11.

⁷³ M Dawidowicz, Third-Party Countermeasures in International Law (CUP 2017); EK Proukaki, The Problem of Enforcement in International Law: Countermeasures, the Non-Injured State and the Idea of International Community (Routledge 2010).

⁷⁴ Barcelona Traction, Light and Power Company, Limited (Belgium v Spain), Judgment [1970] ICJ Rep. 3, para 34.

⁷⁵ ASR (n 21) Commentary to art 54, para 6. The ICJ has also ruled out the use of collective countermeasures; Nicaragua (n 1) para 249. This paragraph was endorsed in Gabčíkovo-Nagymaros Project (Hungary v Slovakia), Judgment [1997] ICJ Rep 7, para 83.

⁷⁶ Dawidowicz (n 73); Proukaki (n 73); Tams (n 69) Ch 6.

⁷⁷ Note that these States used the plural—‘inherent rights’. Presumably, this was because multiple States were invoking the right of self-defence, rather than the fact that multiple, separate legal rights were being advanced.

⁷⁸ GATT Doc C/M/157 (June 27, 1982) 9.

⁷⁹ ‘Article XXI is mentioned as a reflection of unspecified inherent rights, quoting not coincidentally the formulation of article 51 of the UN Charter. It is on these inherent rights that the EC based its action, and not on article XXI, which was mentioned almost as an afterthought’; MJ Hahn, ‘Vital Interests and the Law of GATT: An Analysis of GATT's Security Exception’ (1991) 12 MichiganJIntL 558, 573. See also JL Dewost, ‘La Communauté, les Dix et les “Sanctions” Contre L'Argentine - De la Crise Iranienne à la Crise des Malouines’ (1982) 28 Annuaire Français de Droit International 215, 231 and Kuyper (n 47) 159–62. Tams concludes that the embargoes can be justified on the basis of the right of collective self-defence and as collective countermeasures; Tams (n 69) 216.

⁸⁰ Canadian Practice in International Law during 1982 (n 64) 337.

⁸¹ UN Doc S/14976 (n 61).

⁸² DW Greig, ‘Self-Defence and the Security Council: What Does Article 51 Require?’ (1991) 40 ICLQ 366.

⁸³ UN Doc S/14976 (n 61).

⁸⁴ It is also apparent from the discussions in the GA that members of the international community did not regard the construction of the wall as a prohibited use of force; UNGA A/ES-10/PV.21 (n 11).

⁸⁵ ibid 7. ‘[I]f Israel can resort to forcible measures towards Gaza, this will hold true for any non-forcible measures’; Solomon (n 26) 504.

⁸⁶ Group of Governmental Experts on Advancing Responsible State Behaviour in the Context of International Security, UN Doc A/76/135 (July 14, 2021) para 69; Open-ended Working Group on Developments in the Field of Information and Telecommunications in the Context of International Security, UN Doc A/AC.290/2021/CRP.2 (March 10, 2021) para 34.

⁸⁷ For a discussion of this practice see M Roscini, ‘Cyber Operations as a Use of Force’ in N Tsagourias and R Buchan (eds), Research Handbook on International Law and Cyberspace (Edward Elgar 2021).

⁸⁸ See MN Schmitt, Tallinn Manual 2.0 on the International Law Applicable to Cyber Operations (CUP 2017) Rule 69 and accompanying commentary.

⁸⁹ US Department of Defense, Summary, Department of Defense Cyber Strategy (2018) 1.

⁹⁰ ibid 2.

⁹¹ See Buchan and Tsagourias (n 57) 128–30.

⁹² See the references to Bowett in fn 26.

⁹³ Sicilianos (n 24) 295 (‘This does not mean, however, that the State that is the victim of armed aggression (or its allies) could not react cumulatively by force and by economic or other measures. The latter, if they are in themselves unlawful, will be justified as countermeasures’ (author's translation)). ‘The key feature of the right of self-defence by states is using significant armed force against another state, beyond the defender's own territory. Defensive action not involving significant force is better referred to by other terms, such as intervention, retorsion, and countermeasures’; ME O'Connell, The Art of International Law in the International Community (CUP 2019) 158. ‘If these measures [non-forcible acts of self-defence] involve a breach of the acting State's international obligations then, prima facie, they must purport to be countermeasures’; Scobbie (n 25) 1129. See also Paddeu (n 23) 113.

⁹⁴ As the ILC explains, a State can engage in ‘countermeasures against a State which is responsible for an internationally wrongful act in order to induce that State to comply with its obligations’; ASR (n 21) art 49(1).

⁹⁵ T Ruys, ‘Armed Attack’ and Article 51 of the United Nations Charter: Evolutions in Customary International Law and Practice (CUP 2010) 162; H Kelsen, ‘Unrecht und Unrechtsfragen im Völkerrecht’ (1932) 12 Osterreichische Zeitschrift für öffentliches Recht 481.

⁹⁶ Tams (n 69) 215–16.

⁹⁷ ‘Countermeasures are a feature of a decentralised system by which injured States may seek to vindicate their rights and to restore the legal relationship with the responsible State which has been ruptured by the internationally wrongful act’; ASR (n 21) Commentary to Chapter II, para 1.

⁹⁸ ‘There is, in existing law, a clear distinction to be drawn between two forms of self-help. One, which is of a retributive or punitive nature, is termed ‘retaliation’ or ‘reprisal’ [or a countermeasure]; the other, which is expressly contemplated and authorized by the Charter, is self-defence against armed attack’; United Kingdom (1964) cited in Bowett, ‘Economic Coercion and Reprisals by States’ (n 26) 8. ‘[C]ountermeasures are also distinct from the notion of self-defence … [T]heir purposes are different: countermeasures are a law enforcement tool, whereas self-defence is a defensive reaction designed to restore a certain military balance vis-à-vis an attacking State’; Dawidowicz (n 73) 20. ‘[T]here is undeniably a common element, in that in both cases [of countermeasures and self-defence] the State takes action after having suffered an international wrong, namely, the non-respect of one of its rights by the State against which the action in question is directed or at least in the face of such a danger. But any possible resemblance or true analogy stops at this point … “Self-defence” and “sanction” are reactions relevant to different moments and, above all, are distinct in logic’; Eighth Report (n 17) paras 89–90.

⁹⁹ In the criminal law context, Husak provides a useful distinction between justifications and excuses: ‘Justifications are defenses that arise from properties or characteristics of acts; excuses are defenses that arise from properties or characteristics of actors. A defendant is justified when his conduct is not legally wrongful, even though it apparently violates a criminal law. A defendant is excused when he is not blameworthy or responsible for his conduct, even though it apparently violates a criminal law’; DN Husak, ‘Justifications and the Criminal Liability of Accessories’ (1989) 80 Journal of Criminal Law and Criminology 491, 496 (footnotes omitted). ‘[T]he distinction between warranted and unwarranted action is the critical distinction between justification and excuse’; K Greenawalt, ‘Distinguishing Justifications from Excuses’ (1986) 49 LCP 89, 92. For a similar approach see F Paddeu, Justification and Excuse in International Law: Concept and Theory of General Defences (CUP 2018) Ch 3.

¹⁰⁰ ‘[S]elf-defence is recognized as a primary rule in customary law and in Article 51 of the UN Charter which recognizes self-defence as an inherent right. As a right, it empowers states to use force and such force is lawful per se; it is not a prima facie violation of the prohibition of the use of force enshrined in Article 2(4) of the UN Charter which is subsequently exonerated’; Tsagourias (n 22) 813. See also Paddeu (n 99) Ch 5 and GM Badr, ‘The Exculpatory Effect of Self-Defense in State Responsibility’ (1980) 10 GaJIntl&CompL 1.

¹⁰¹ ASR (n 21) Commentary to art 21, para 1 (‘a State exercising its inherent right of self-defence as referred to in Article 51 of the Charter is not, even potentially, in breach of Article 2, paragraph 4’).

¹⁰² S Wittich, ‘The International Law Commission's Articles on the Responsibility of States for Internationally Wrongful Acts Adopted on Second Reading’ (2002) 15 LJIL 891, 898.

¹⁰³ ‘Throughout the draft articles, the Commission has made clear its conviction that a distinction must be drawn between the idea of wrongfulness, expressing the fact that certain conduct by a State conflicts with an obligation imposed on that State by a “primary” rule of international law, and the idea of responsibility, indicating the legal consequences which another, “secondary” rule of international law attaches to the act of the State that such conduct consists of. On the basis of that conviction, there is no reason, at least in theory, why certain circumstances should not preclude responsibility without at the same time precluding wrongfulness’; International Law Commission, Eighth Report on State Responsibility by Mr Roberto Ago, UN Doc A/CN.4/318 and Add 1-4 (1976) para 50. ‘Taking stock of the ILC work on the classification of defences reviewed earlier, it is reasonable to conclude that the title ‘circumstances precluding wrongfulness’ in the text of the ARS does not entail that the listed defences all operate as justifications’; Paddeu (n 99) 50.

¹⁰⁴ ASR (n 21) Commentary to Chapter V, para 2 (‘[The circumstances precluding wrongfulness] do not annul or terminate the obligation; rather they provide a justification or excuse for non-performance while the circumstance in question subsists’). See also para 8 (‘Where conduct in conflict with an international obligation is attributable to a State and that State seeks to avoid its responsibility by relying on a circumstance under chapter V, however, the position changes and the onus lies on that State to justify or excuse its conduct’).

¹⁰⁵ ‘At the outset of this discussion of chapter V, it was noted that the circumstances dealt with probably fell into several categories, and that at least with respect to certain of them it might be more appropriate to speak of circumstances precluding responsibility than wrongfulness. At least with respect to force majeure, distress and necessity, an alternative formulation for the purposes of chapter V might be “A State is not responsible for its failure to perform an international obligation if the failure is due to” one of those circumstances. This could contrast with the formulation in the case of self-defence, and possibly countermeasures, where it could be said that the circumstance precludes wrongfulness’; Second Report on State Responsibility by Mr James Crawford (n 18) para 355.

¹⁰⁶ ‘[T]he legality of countermeasures derives from the fact that the wrongdoing state has, by its conduct, forfeited the legal protection of its rights. As a result, when the injured state adopts countermeasures against it, it does not breach the target state's rights since the target state has forfeited the law's protection of those rights’; Paddeu (n 99) 276.

¹⁰⁷ ibid 227 (‘countermeasures can only be classified as justifications: the countermeasure constitutes at most prima facie or apparent breach of the obligation affected, a breach that is precluded by the circumstances in which the measure is adopted’).

¹⁰⁸ O'Connell (n 24) 249 (‘Arguably, these [countermeasures] are better thought of as excuses rather than “circumstances precluding wrongfulness”’). France has also endorsed this view: see UN Doc A/C.6/56/SR.11 (November 9, 2001) para 70.

¹⁰⁹ Paddeu (n 99) 282.

¹¹⁰ ‘Generally, the range of possible situations covered by chapter V is such that to lay down a detailed regime for compensation is not appropriate. It will be for the State invoking a circumstance precluding wrongfulness to agree with any affected States on the possibility and extent of compensation payable in a given case’; ASR (n 21) Commentary to art 27, para 6.

¹¹¹ TM Franck, Recourse to Force: State Action Against Threats and Armed Attacks (CUP 2002) 191.

¹¹² K Greenawalt, ‘The Perplexing Borders of Justification and Excuse’ (1984) 84 ColumLRev 1897, 1898.

¹¹³ V Lowe, ‘Precluding Wrongfulness or Responsibility: A Plea for Excuses’ (1999) 10 EJIL 405, 406.

¹¹⁴ Third-party countermeasures must be distinguished from collective countermeasures. While there is legitimate debate as to whether States can take collective countermeasures to defend community obligations, there is no suggestion within State practice that injured States can request non-injured States to take countermeasures on their behalf in order to enforce compliance with bilateral obligations; Dawidowicz (n 73) Ch 4.

¹¹⁵ Art 51 UN Charter; Nicaragua (n 1) para 194.

¹¹⁶ JD Ohlin, ‘The Doctrine of Legitimate Defense’ (2015) 91 International Law Studies 119, 141 (citations omitted). ‘In international law, then, it seems that justification and excuse can have an impact on the responsibility of accessories: justifications affect the responsibility of accessories to it and, in this sense, they have a universalist tendency; excuses, in contrast, are individualist in tendency, insofar as they attach only to the invoking state’; Paddeu (n 99) 70.

¹¹⁷ ‘The wrongfulness of an act of a state not in conformity with an international obligation towards another State is precluded if and to the extent that the act constitutes a countermeasure taken against the latter State’; ASR (n 21) art 22 (emphasis added).

¹¹⁸ ‘[There is] nothing in the text of Article 51 that thus stipulates that self-defence is available only when an armed attack is made by a State’; Wall (n 14) para 33 (Separate Opinion of Judge Higgins).

¹¹⁹ UNSC Res. 1368 (2001); UNSC Res. 1373 (2001). For a review of this State practice see TD Gill and K Tibori-Szabó, ‘Twelve Key Questions on Self-Defense against Non-State Actors’ (2020) 95 International Law Studies 467, 479–90 and, more generally, CJ Tams, ‘The Use of Force against Terrorists’ (2009) 20 EJIL 359. But for a different view see Wall (n 14) para 139 (where the ICJ held that art 51 UN Charter ‘recognizes the existence of an inherent right of self-defence in the case of armed attack by one State against another State’).

¹²⁰ ‘In the first place it must be taken in response to a previous international wrongful act of another State’; Gabčíkovo-Nagymaros (n 75) para 83 (emphasis added).

¹²¹ ‘Imminent threats are fully covered in Article 51, which safeguards the inherent right of sovereign States to defend themselves against an armed attack. Lawyers have long recognized that this covers an imminent attack as well as one that has already happened’; Report of the UN Secretary-General, In Larger Freedom: Towards Development, Security and Human Rights For All, UN Doc A/59/2005 (March 21, 2005) para 124.

¹²² ‘Reprisals are only legitimate in response to an international delinquency on the part of another State. For self-defence it is enough that there should be a threat of injury which it is impossible otherwise to avert in time’; HM Waldock, ‘The Regulation of the Use of Force by Individual States in International Law’ (1952) 81 Recueil des Cours 464.

¹²³ Armed attacks by non-State actors, for example, may not qualify as unlawful uses of force.

¹²⁴ ASR (n 21) art 52(1)(b).

¹²⁵ ‘[An] injured State may take such urgent countermeasures as are necessary to preserve its rights’; ibid, art 52(2).

¹²⁶ While art 51 UN Charter requires States to notify the SC when they engage their right of self-defence, this obligation applies only after defensive action has been taken.

¹²⁷ ASR (n 21) art 49(3).

¹²⁸ ‘Countermeasures shall, as far as possible, be taken in such a way as to permit the resumption of performance of the obligations in question’; ibid, art 49(3). ‘States should as far as possible choose countermeasures that are reversible’; ibid, Commentary to art 49, para 9. ‘[S]ince countermeasures are intended as instrumental—in other words, since they are taken with a view to procuring cessation of and reparation for the internationally wrongful act and not by way of punishment—they are temporary in character and must be as far as possible reversible in their effects in terms of future legal relations between the two States’; ibid Introduction to the Commentary to Chapter II (Countermeasures), para 6.

¹²⁹ ibid Commentary to art 49, para 9.

¹³⁰ ibid art 49(1).

¹³¹ Nicaragua (n 1) para 176; Nuclear Weapons (n 3) para 41; Oil Platforms (n 3) paras 76–77.

¹³² ASR (n 21) art 51.

¹³³ Nicaragua (n 1) para 176; Nuclear Weapons (n 3) para 41; Oil Platforms (n 3) paras 76–77.

¹³⁴ ASR (n 21) art 51. See also Gabčíkovo-Nagymaros (n 75) para 85.

¹³⁵ ASR (n 21) Commentary to art 51, para 6.

¹³⁶ ‘It is generally agreed that all counter-measures must, in the first instance, have some degree of equivalence with the alleged breach; this is a well-known rule’; Air Service Agreement of 27 March 1946 between the United States of America and France (December 9, 1978) Vol. XVIIII 417, para 83.

¹³⁷ ‘[E]ven if one were to admit that the law of nations does not require that the reprisal should be approximately in keeping with the offence, one should certainly consider as excessive and therefore unlawful reprisals out of all proportion to the act motivating them’; Portuguese Colonies Case (Naulilaa incident), UNRIAA, Vol. II (Sales No. 1949.V.1) 1011, 1028. See also ASR (n 21) Commentary to art 51, para 6.

¹³⁸ ‘[Proportionality] calls for a balance to be struck between the need to repel the attack and the harm that defensive military action is likely to result in for other values and interests at stake, such as values of a humanitarian nature’; E Cannizzaro, ‘Contextualising Proportionality: Jus ad Bellum and Jus in Bello in the Lebanese War’ (2006) 88 International Review of the Red Cross 779, 784.

¹³⁹ Ruys (n 95) 110–23.

¹⁴⁰ D Kretzmer, ‘The Inherent Right of Self-Defence and Proportionality in Jus Ad Bellum’ (2013) 24 EJIL 235, 278.

¹⁴¹ D Bethlehem, ‘Self-Defense Against an Imminent or Actual Armed Attack by Nonstate Actors’ (2012) 106 AJIL 770, 775.

¹⁴² Ruys (n 95) 123; Kretzmer (n 140) 282; G Nolte and A Randelzhofer, ‘Article 51’ in B Simma, D-E Khan, G Nolte and A Paulus (eds), The Charter of the United Nations: A Commentary (OUP 2012) 1425.

¹⁴³ For an overview see N Ronzitti, ‘The Expanding Law of Self-Defence’ (2006) 11 JC&SL 343.

¹⁴⁴ US Department of State, Harold H Koh (Legal Advisor), International Law in Cyberspace (September 18, 2012). For academic support for this approach see R Higgins, Problems and Process: International Law and How We Use It (Clarendon Press 1994) 221.

¹⁴⁵ Office of the White House, The National Security Strategy of the United States of America (September 2002). For academic support for this argument see M Glennon, ‘The Fog of Law: Self-Defense, Inherence, and Incoherence in Article 51 of the United Nations Charter’ (2002) 25 Harvard Journal of Law and Public Policy 539.

¹⁴⁶ See eg, J Kammerhofer, ‘The Resilience of the Restrictivist Rules of Self-Defence’ in M Weller (ed), The Oxford Handbook on the Use of Force in International Law (OUP 2014).