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The permissive power of the ban on war

  • Ian Hurd (a1)


The ban on inter-state war in the UN Charter is widely identified as central to the modern international order–Michael Byers calls it ‘one of the twentieth century’s greatest achievements’. Even if it is only imperfectly observed, it is often seen as a constraint on state autonomy and an improvement on the pre-legal, unregulated world before 1945. In response to this conventional view, this article shows that the laws on war in the Charter are better seen as permissive rather than constraining. I make two points. First, by creating a legal category around ‘self-defence’, the laws on war authorise, and thus legitimate, wars that are motivated by the security needs of the state, while forbidding other motives for wars. Second, state practice since 1945 has expanded the scope of this authorisation, extending it in both time and space beyond the black-letter text of the Charter. The permissive effect of law on war has therefore been getting larger. These two effects suggest that international law is a resource that increases state power, at least for powerful states, and this relation between international law and power politics is missed by both realists and liberal internationalists.


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*Correspondence to: Ian Hurd, Associate Professor (also Legal Studies And Director, International Studies Program), Department of Political Science, Northwestern University – Political Science, Evanston 60208, United States. Author’s email:


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1 Sir Pollock, Frederick and Maitland, Frederic William, The History of English Law Before the Time of Edward I (2nd edn, Cambridge: Cambridge University Press, 1899), p. 449 , cited in Smith, Caleb, The Prison and the American Imagination (New Haven: Yale University Press, 2009), p. 30 .

2 Ruys, Tom, ‘Armed Attack’ and Article 51 of the UN Charter: Evolutions in Customary Law and Practice (Cambridge: Cambridge University Press, 2010), p. 11 .

3 Byers, Michael, War Law (New York: Atlantic Books, 2005), p. 148 . See also, O’Connell, , ‘Peace and war’, in Bardo Fassbender and Anne Peters (eds), The Oxford Handbook of the History of International Law (Oxford: Oxford University Press, 2012).

4 See, for instance, Ikenberry, G. John and Slaughter, Anne-Marie, Princeton Project on National Security (Woodrow Wilson School, Princeton University, 2006), available at: {}.

5 The expansion of international legal institutions and forms in the late twentieth century gives strong states another means by which to exercise power over other actors in the international system. Reus-Smit, Christian, American Power and World Order (London: Polity, 2004); Scott, Shirley V., International Law, US Power: The United States’ Quest for Legal Security (Cambridge: Cambridge University Press, 2012); Kennedy, David, The Dark Side of Virtue: Reassessing International Humanitarianism (Princeton: Princeton University Press, 2004); Fisk, Kerstin and Ramos, Jennifer M., ‘Actions speak louder than words: Preventative self-defense as a cascading norm’, International Studies Perspectives, 15:2 (May 2014), pp. 163185 .

6 Kinsella, Helen M., The Image Before the Weapon: A Critical History of the Distinction between Combatant and Civilian (Ithaca, NY: Cornell University Press, 2011); Harcourt, Bernard, The Illusion of Free Markets: Punishment and the Myth of Natural Order (Cambridge, MA: Harvard University Press, 2012).

7 On this see Scott, Shirley V., International Law, US Power: The United States’ Quest for Legal Security (Cambridge: Cambridge University Press, 2012); Schachter, Oscar, ‘The legality of pro-democratic intervention’, American Journal of International Law, 78:3 (1984), pp. 645650 (p. 648).

8 Hurd, Ian, After Anarchy: Power and Legitimacy in the UN Security Council (Princeton: Princeton University Press, 2007).

9 The Kellogg-Briand Pact (also known as the Pact of Paris, and more formally as the General Treaty for the Renunciation of War as an Instrument of National Policy) was for a time the most widely ratified international instrument. It bans war by its parties in their relations among each other but leaves unaffected their wars with others. The treaty has just two operative paragraphs, which require that parties ‘condemn the recourse to war for the solution of international controversies, and renounce it as an instrument of national policy in their relations with one another’ (Article I) and ‘agree that the settlement or solution of all disputes or conflicts, of whatever nature or of whatever origin they may be, which may arise among them, shall never be sought except by pacific means’ (Article II). It remains in effect today among its signatories.

10 See the discussion in Alexandrov, Stanimir A., Self-Defense Against the Use of Force in International Law (The Hague: Kluwer, 1996).

11 The recent wave of scholarly interest at the boundary between political science and legal studies on the ‘legalisation’ of world politics has not addressed this case. It is not among the central cases in, for instance, Goldstein, Judith L., Kahler, Miles, Keohane, Robert O., and Slaughter, Anne-Marie (eds), Legalization and World Politics (Cambridge, MA: MIT Press, 2001); Dunoff, Jeffrey L. and Pollack, Mark A. (eds), Interdisciplinary Perspectives on International Law and International Relations: The State of the Art (Cambridge: Cambridge University Press, 2013); or Halliday, Terence C. and Shaffer, Gregory (eds), Transnational Legal Orders (Cambridge: Cambridge University Press, 2015). Also see Oona Hathaway and Scott Shapiro, The Worst Crime of All (Simon and Shuster, 2017).

12 Ruys, , ‘Armed Attack’ and Article 51 of the UN Charter, p. 11 .

13 Hathaway and Shapiro, The Worst Crime of All.

14 Finnemore, Martha, The Purpose of Intervention: Changing Beliefs about the Use of Force (Ithaca: Cornell University Press, 2004).

15 Byers, Michael, War Law: Understanding International Law in Armed Conflict (New York: Grove Press, 2005); Hathaway and Shapiro, The Worst Crime of All. See also, Jennifer Mitzen’s account of European ‘stability’ governed by the Concert of Europe, in Mitzen, Jennifer, Power in Concert: The Nineteenth-Century Origins of Global Governance (Chicago: University of Chicago Press, 2013).

16 Gray, Christine, International Law and the Use of Force (3rd edn, Oxford: Oxford University Press, 2008), p. 6 .

17 Byers, Michael, ‘Jumping the gun’, London Review of Books, 24:14 (2002), pp. 35 .

18 Franck, Thomas M., Recourse to Force: State Action Against Threats and Armed Attacks (Cambridge: Cambridge University Press, 2002), p. 10 .

19 The naïve version assumes that changing the law will necessarily change behaviour accordingly. This is a straw target, easier to caricature than to actually find in scholarship. The original statement of world peace through law is Clark, Grenville and Sohn, Louis B., World Peace Through World Law (Cambridge, MA: Harvard University Press, 1958). Debunking the myth of legal naïvety in relation to the 1928 Kellogg-Briand Pact, see Josephson, Harold, ‘Outlawing war: Internationalism and the Pact of Paris’, Diplomatic History, 3:4 (1999), pp. 377390 .

20 Bull, Hedley, The Anarchical Society: A Study in World Order (3rd edn, New York: Columbia University Press, 2002).

21 Lauterpacht, Hersch, The Function of Law in the International Community (Oxford: Oxford University Press, 1933), p. 64 , cited in Franck, Recourse to Force, p. 1.

22 O’Connell‚ ‘Peace and war’, p. 272. Rosa Brooks says ‘at its most fundamental level, the rule of law is concerned with constraining and ordering power and violence’. See Brooks, Rosa, ‘Drones and the international rule of law’, Ethics and International Affairs, 28:1 (2014), p. 83 .

23 Compare this to, for instance, Leo Strauss, who suggests ‘the broader consideration of what law is for, namely the existence, preferably on a high level, of political society as a whole’, not just the regulation of violence. Leo Strauss in ‘Seminar on The Philosophy of History’, quoted in Howse, Robert, Leo Strauss: Man of Peace (Cambridge: Cambridge University Press, 2014), p. 130 .

24 Ikenberry, G. John, Liberal Leviathan: The Origins, Crisis, and Transformation of the American World Order (Princeton: Princeton University Press, 2011), p. 106 .

25 Ibid., p. 18. See also Brooks, Stephen G., Ikenberry, G. John, and Wohlforth, William C., ‘Lean forward: In defense of American engagement’, Foreign Affairs, 92:1 (Jan/Feb 2013),

26 Ikenberry, Liberal Leviathan, p. 84.

27 Ibid., p. 21.

28 Nau, Henry R., Conservative Internationalism: Armed Diplomacy under Jefferson, Polk, Truman, and Reagan (Princeton: Princeton University Press, 2014), p. 228 . He identifies Iran as a ‘threat’ to world order because it exhibits ‘less respect for international rules’ than the US does (p. 231). He also says that the US ‘failure’ to use the collective self-defence provisions of the NATO charter (Art. V) was a mistake of historic proportions, ‘one of the great mysteries and tragedies of the history of 9/11’, p. 237.

29 Nau, Conservative Internationalism, p. 232.

30 Hardt, Michael and Negri, Antonio, Empire (Cambridge, MA: Harvard University Press, 2000), p. 14 . Also, Brunkhorst, Hauke, Critical Theory of Legal Revolutions: Evolutionary Perspectives (London: Bloomsbury Academic, 2014), esp. 3.IV.

31 See also Chimni, B. S., ‘International institutions today: an imperial global state in the making’, European Journal of International Law, 15:1 (2004), pp. 137 .

32 Hardt and Negri, Empire, p.18.

33 Ibid., p. 15.

34 Mitzen, Power in Concert; Sharp, Paul, Diplomatic Theory of International Relations (Cambridge: Cambridge University Press, 2009).

35 See, for instance, Guzman, Andrew, How International Law Works: A Rational Choice Theory (Oxford: Oxford University Press, 2010).

36 This is based in part on the hierarchy of legal sources set out in Article 38(1) of the Statute of the International Court of Justice, and in part on customary law and state practice. See Greenwood, Christopher, ‘The Sources of International Law: An Introduction’, available at: {} accessed 5 May 2016.

37 Several book-length treatments exist including Gray, International Law and the Use of Force; Franck, Recourse to Force; O’Connell, ‘Peace and war’. On self-defence in particular, see Alexandrov, Self-Defense Against the Use of Force in International Law.

38 This is set out in the Vienna Convention on the Law of Treaties (1969) at Article 31(1).

39 See The United Nations Yearbook (New York: United Nations, 1982), pp. 1319–47.

41 For contestation over this among American legal scholars, see the essays in ‘Agora: Future implications of the Iraq Conflict’, in the American Journal of International Law, 97:3 (2003).

42 Michael Byers provides a rare exception in Byers, ‘Jumping the gun’, p. 5 where he says ‘the UN Charter provides a clear answer to these questions: in the absence of an armed attack, the Security Council alone can act.’ This is at odd with Byers’s analysis in War Law, and reflects perhaps the fact that for Byers the US invasion of Iraq was not the sort of war which should be legitimated by finding it to be legal under the Charter.

43 See Ruys, ‘Armed Attack’ and Article 51 of the UN Charter, p. 1; Corten, Olivier, ‘The controversies over the customary prohibition on the use of force: a methodological debate’, European Journal of International Law, 16:5 (2006), pp. 803822 ; Hollis, Duncan B., ‘The existential function of interpretation in international law’, Temple University Legal Studies Research Paper Series, 2013:43 (2013); Venzke, Ingo, ‘Is interpretation in international law a game?’, in Andrea Bianchi, Daniel Peat, and Matthew Windsor (eds), Interpretation in International Law (Oxford: Oxford University Press, 2014); Orakhelashvili, Alexander, The Interpretation of Acts and Rules in Public International Law (Oxford: Oxford University Press 2008); and essays in Hollis, Duncan B. (ed.), The Oxford Guide to Treaties (Oxford: Oxford University Press, 2012).

44 Franck, Recourse to Force, p. 51.

45 On legal interpretation see Orakhelashvili, The Interpretation of Acts and Rules in Public International Law, and the analyses in Venzke, Ingo, How Interpretation Makes International Law (Oxford: Oxford University Press, 2012), and Duncan B. Hollis, ‘The existential function of international law’, in Bianchi, Peat, and Windsor (eds), Interpretation in International Law. See also, Katharina Berner, ‘Authentic interpretation in public international law’, manuscript presented to the Rule of Law Center, Berlin Social Science Center (WZB) (2014). Hollis says ‘International law does not exist without interpretation.’ (p. 1). Also Keitner, Chimène I., ‘“Cheap talk” about customary law’, in David L. Sloss, Michael D. Ramsay, and William S. Dodge (eds), International Law and the U.S. Supreme Court (Cambridge: Cambridge University Press, 2011).

46 See the references in Schachter, Oscar, ‘Self-defense and the rule of law’, The American Journal of International Law, 83:2 (1989), pp. 259277 (p. 263, fn. 22). See also, Franck, Recourse to Force, p. 50.

47 In both the Iraq-Kuwait war in 1990 and the Afghanistan war in 2001, for instance, the states invoking self-defence did not defer to the Council and the Council followed up by affirming their right not to do so.

48 See, among others, Ikenberry, Liberal Leviathan, p. 259: ‘The notion that states have a right of self-defense in the face of an “imminent threat” was widely recognized in international law and diplomacy.’ The consensus around this even includes scholars who are otherwise committed to a literal reading of the Charter. Oscar Schachter, as an example, is generally opposed to ‘expanded conceptions of self-defense’ but he finds it unproblematic to say that there is ‘strong resistance to widening self-defense to permit force except where there has been an armed attack or threat of armed attack’ (emphasis added). By accepting the legality of anticipatory self-defence, he is accepting the ‘expanded’ conception and arguing in effect that it should not be expanded any further. Schachter, ‘Self-defense and the rule of law’, pp. 271, 273.

49 Variations, of course, exist. The idea of ‘imminence’ is often derived from Daniel Webster, who said that anticipatory acts are acceptable when ‘the necessity of that self-defence is instant, overwhelming, and leaving no choice of means, and no moment of deliberation’. See Webster, Daniel, ‘Letter to Henry Stephen Fox’, in K. E. Shewmaker (ed.), The Papers of Daniel Webster: Diplomatic Papers, 1841–1843, Volume 1 (Hanover, NH: Dartmouth College Press, 1983).

50 The issue of ‘anticipation’ came up in 1945 and was struck down by the Five Powers who dominated the Charter-drafting process. The US considered the issue internally in its delegation and Harold Stassen expressed the definitive official position against it: ‘this was intentional … we did not want exercised the right of self-defense before an armed attack had occurred’. Ruys, ‘Armed Attack’ and Article 51 of the UN Charter, p. 65. citing Foreign Relations of the United States (1945), p. 818.

51 It is in fact integral to treaty interpretation in international law. See the essays in Nolte, Georg (ed.), Treaties and Subsequent Practice (Oxford: Oxford University Press, 2013).

52 Franck, Recourse to Force, p. 21.

53 Reisman, W. Michael, ‘Coercion and self-determination: Construing Article 2(4)’, American Journal of International Law, 78:3 (1984), pp. 642645 (p. 644).

54 Reisman, ‘Coercion and self-determination’, p. 645.

55 Ruys, ‘Armed Attack’ and Article 51 of the UN Charter, p. 511.

56 Franck, Recourse to Force, p. 21.

57 Byers, War Law, p. 60.

58 Ruys, ‘Armed Attack’ and Article 51 of the UN Charter, p. 6. It is through this process that many states and scholars have argued that humanitarian intervention has become a legal form of international military action. As states have come to see humanitarian intervention as desirable, they have consequently argued that it is legal under the Charter. Belgium made this argument at the International Court of Justice in the Legality of the Use of Force case, as did the United Kingdom in relation to the Kosovo bombing: ‘The action being taken is legal. It is justified as an exceptional measure to prevent an overwhelming humanitarian catastrophe … . In these circumstances, military intervention is legally justifiable.’ See Gray, International Law and the Use of Force, p. 42.

59 Franck, Recourse to Force, p. 49.

60 Reisman, ‘Coercion and self-determination’, p. 644.

61 Klabbers, Jan, An Introduction to International Institutional Law (2nd edn, Cambridge: Cambridge University Press, 2009), p. 218 , cited by Ramses Wessel in Cogan, Jacob Katz, Hurd, Ian, and Johnstone, Ian (eds), Oxford Handbook of International Organizations (Oxford: Oxford University Press, 2016 [forthcoming]).

62 On the ‘uses of history’, see Moyn, Sam, Human Rights and the Uses of History (London: Verso, 2014).

63 Schachter, ‘Self-defense and the rule of law’, p. 268.

64 The phrase comes from Strauss’s discussion of Thucydides presented in Howse, Leo Strauss, p. 135.

65 International Court of Justice (ICJ), Nicaragua, Summary of Judgment, para. 2, available at: {} accessed 5 May 2016.

66 This mirrors a shift in realist thinking about international relations from a ‘balance against power’ model to a ‘balance against threat’ model, following Walt, Stephen M., ‘Alliance formation and the balance of power’, International Security, 9:4 (1985), pp. 343 .

67 On Entebbe, see the debate between Sheenan, Jeffrey A., ‘The Entebbe Raid: the principle of self-help as justification for state use of Armed Force’, The Fletcher Forum, 1:1 (1977), pp. 135153 ; and Paust, Jordan J., ‘Entebbe and self-help: the Israeli response to terrorism’, The Fletcher Forum, 2:1 (1978), pp. 8692 . On military action on behalf of citizens abroad see Ruys, ‘Armed Attack’ and Article 51 of the UN Charter.

68 United States Department of Justice, ‘Attorney General Eric Holder Speaks at Northwestern University Law School’ (5 March 2012), available at: {} accessed 5 May 2016.

69 Alexandrov, Self-Defense Against the Use of Force in International Law, ch. 17. See also Schachter’s justification of American military action against ‘sharp local deviations’ from US preferences in South American governments, in Henkin, Louis, ‘Reports of the death of Article 2(4) are greatly exaggerated’, American Journal of International Law, 65:3 (1979), pp. 544548 (p. 546).

70 NATO, ‘NATO Ten Years After: Learning the Lessons’ (11 September 2011), available at: {}.

71 Kinsella, The Image Before the Weapon.

72 Consider a passage from Louis Henkin, as he argued in 1971 that Article 2(4) had been influential in shaping American foreign policy. He said ‘few believe that the OAS [Organization of American States] or even the United States alone would use force against the political independence or territorial integrity of any country in the [Western] Hemisphere, even in the event of sharp local deviation, if it was not in fact abetted from the outside.’ Henkin meant this to show how profoundly the ban on war had been internalised in American foreign policy. He believed American decision-makers would find it hard to justify violating it. But at the same time he saw ‘outside’ influence over ‘local deviations’ to be sufficient justification for lawful American intervention. He appeared to think that the ban on war protected states from American intervention as long as they remained on line with American preferences regarding their policies. For Henkin, then, the use of force by the US in Latin America was not prohibited by Article 2(4) if it was a response to Soviet or other ‘outside’ actions there. Henkin, ‘Reports of the death of Article 2(4) are greatly exaggerated’, pp. 544–8 (p. 546).

73 On ‘after’, consider that the US attacks on Libya in 1986 were characterised as ‘self-defence’ after Libyan attacks on various US interests around the world including the Berlin disco bombing but took place some ten days after the disco bombing on 5 April of that year.

74 D’Amato says self-defence is ‘a loophole that gets wider the more one looks at it’. D’Amato, Anthony, ‘The invasion of Panama was a lawful response to tyranny’, American Journal of International Law, 84:2 (1990), pp. 516524 .

75 Hurd, Ian, ‘The international rule of law and the domestic analogy’, Global Constitutionalism, 4:3 (2015), pp. 365395 .

76 On the first, see Guzman, How International Law Works. On the second, see Hathaway, Oona, ‘Do human rights treaties make a difference?’, The Yale Law Journal, 111:8 (2001–2), pp. 19352042 .

77 Byers, War Law, p. 2.

78 Franck, Recourse to Force, p. 9.

79 Raz, Joseph, ‘Reasons: Practical and adaptive’, in David Sobel and Steven Wall (eds), Reasons for Action (Cambridge: Cambridge University Press, 2011).

80 See D’Amato, ‘The invasion of Panama was a lawful response to tyranny’ on pro-democracy intervention; Franck, Recourse to Force on humanitarian intervention; and Evans, Gareth and Sahnoun, Mohamed, ‘The Responsibilty to Protect’, Foreign Affairs, 81:6 (2002), pp. 99110 on Responsibility to Protect.

81 Taylor, Charles, ‘To follow a rule…’, in Craig Calhoun, Edward LiPuma, and Moische Postone (eds), Bourdieu: Critical Perspectives (Chicago: University of Chicago Press, 1993); Friedrich V. Kratochwil, Rules, Norms, and Decisions: On the Conditions of Practical and Legal Reasoning in International Relations and Domestic Affairs (Cambridge: Cambridge University Press, 1989).

82 Finnemore, The Purpose of Intervention.

83 Waltz, Kenneth N., Theory of International Politics (New York: McGraw-Hill, 1979).

84 Franck, Thomas, ‘Who killed Article 2(4)? or: Changing norms governing the use of force by states’, American Journal of International Law, 64:5 (1970), pp. 809837 ; Glennon, Michael, ‘The fog of law: Self-defense, inherence, and incoherence in Article 51 of the United Nations Charter’, Harvard Journal of Law and Public Policy, 25:2 (2002), pp. 539558 (p. 540).

85 Niccolò Machiavelli, The Prince (1532), ch. 26 cited in O’Connell, ‘Peace and war’, p. 275.

86 Marx, Karl, ‘For a ruthless criticism of everything existing’ [also known as ‘Letter from Marx to Arnold Ruge’] in Robert C. Tucker (ed.), The Marx-Engels Reader (2nd edn, New York: Norton, 1978), p. 15 .

87 Reisman, ‘Coercion and self-determination’, p. 643.

88 Ruys, ‘Armed Attack’ and Article 51 of the UN Charter, p. 4.

89 Byers, War Law, p. 155. See also the ICJ Nicaragua expectation that ‘the conduct of States should, in general, be consistent with such rules’ rather than that ‘the application of the rules in question should have been perfect’. Nicaragua case, para. 186, cited in Gray, International Law and the Use of Force, p. 25

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