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Proportionality under Jus ad Bellum and Jus in Bello: Clarifying their Relationship

  • Raphaël van Steenberghe (a1)

Proportionality is a condition provided under both jus ad bellum and jus in bello. Based on a particular interpretation of state practice and international case law, recent legal literature argues that the two notions of proportionality are interrelated in that proportionality under jus in bello is included in the assessment of proportionality under jus ad bellum. This article seeks to refute such a position and, more generally, to clarify the relationship between the two notions of proportionality.

The main argument of the article is in line with the traditional position regarding the relationship between jus ad bellum and jus in bello. It is argued that, although sharing common features and being somewhat interconnected, the notions of proportionality provided under these two separate branches of international law remain independent of each other, mainly because of what is referred to in this article as the ‘general versus particular’ dichotomy, which characterises their relations. Proportionality under jus ad bellum is to be measured against the military operation as a whole, whereas proportionality under jus in bello is to be assessed against individual military attacks launched in the framework of this operation.

This article nonetheless emphasises the risk of overlap between the assessments of the two notions of proportionality when the use of force involves only one or a few military operations. Indeed, in such situations, the ‘general versus particular’ dichotomy, which normally enables one to make a distinct assessment between the two notions of proportionality, is no longer applicable since it becomes impossible to distinguish between the military operation as a whole and the individual military attacks undertaken during this operation.

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1 See nn 7 and 8.

2 See, for example, Kolb Robert, Ius in bello: Le droit international des conflits armés (2nd edn, Helbing Lichtenhahn 2009) 3638.

3 See, for example, Meyrowitz Henri, Le principe de l'égalité des belligérants devant le droit de la guerre (Pedone 1970) 77. See, in particular, the debates within the International Law Institute in 1963 on the question of equal application of the laws of war to parties to an armed conflict, (1963) 50 Annuaire de l'Institut de Droit International 306.

4 See, for instance, Sassòli Marco, Bouvier Antoine A and Quintin Anne, How Does Law Protect in War (3rd edn, ICRC 2011) 115.

5 See, for example, Kolb (n 2) 72.

6 See the Preamble to the Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts (entered into force 7 December 1978) 1125 UNTS 3 (‘Additional Protocol I’); see also art 96, para (3) of the same Protocol.

7 See, for example, Meyrowitz (n 3); Sassòli, Bouvier and Quintin (n 4) 114–16; Sassòli Marco, ‘Ius ad Bellum and Ius in Bello – The Separation between the Legality of the Use of Force and Humanitarian Rules to be Respected in Warfare: Crucial or Outdated?’ in Schmitt Michael N and Pejic Jelena (eds), International Law and Armed Conflict: Exploring the Faultlines. Essays in Honour of Yoram Dinstein (Martinus Nijhoff 2007) 242; Kolb (n 2) 17; David Eric, Principes de droit des conflits armés (4th edn, Bruylant 2008) 613; Roberts Adam, ‘The Equal Application of the Laws of War: A Principle under Pressure’ (2008) 90 International Review of the Red Cross 931; Giladi Rotem, ‘The Jus ad Bellum/Jus in Bello Distinction and the Law of Occupation’ (2008) 41 Israel Law Review 246; Moussa Jasmine, ‘Can Jus ad Bellum Override Jus in Bello? Reaffirming the Separation of the Two Bodies of Law’ (2008) 90 International Review of the Red Cross 963.

8 See, for example, ICTY, Prosecutor v Boškoski, Judgment, IT-04-82-A, Appeals Chamber, 19 May 2010, [51]; see also Juan Carlos Abella, Argentina, Recommendations 11.137, Inter-American Commission on Human Rights, OEA/Ser.L/V/II.98 doc 6 rev, 13 April 1998, paras 173–74, available at See, for instance, regarding national case law, Danikovic and Others v State of the Netherlands (2004) 35 Netherlands Yearbook of International Law 522, 524.

9 See, for instance, Orakhelashvili Alexander, ‘Overlap and Convergence: The Interaction between Jus ad Bellum and Jus in Bello’ (2007) 12 Journal of Conflict and Security Law 157; Sharma Serena K, ‘Reconsidering the Jus ad Bellum/Jus in Bello Distinction’ in Stahn Carsten and Kleffner Jann K (eds), Jus Post Bellum: Towards a Law of Transition from Conflict to Peace (TC Asser 2008) 9.

10 Sharma, ibid.

11 See nn 25, 30, 32 and 33.

12 See, for example, Chinkin Christine M, ‘Kosovo: A “Good” or “Bad” War?’ (1999) 93 American Journal of International Law 841, 841–42; Charney Jonathan I, ‘Anticipatory Humanitarian Intervention in Kosovo’ (1999) 93 American Journal of International Law 834, 839. In this case, proportionality would be measured between the humanitarian intervention and the purpose of protecting the civilian populations.

13 See, for example, Simma Bruno (ed), The Charter of the United Nations: A Commentary (OUP 1994) 631. In this case, proportionality would be measured between the UNSC military action and the general objective that this action is authorised to pursue according to the relevant UNSC resolution (see, for state practice in this sense, n 14).

14 In some instances, states have criticised the military action undertaken on the basis of an express UNSC authorisation by emphasising the disproportionate nature of such action; see, in this respect, some state reactions to the military action conducted by the allies in Iraq on the basis of UNSC Resolution 678 (29 November 1990), Keesing's Contemporary Archives (1991) 37989; see also the recent Russian declarations considering the 2011 NATO military action in Libya to be disproportionate because it exceeded the mandate provided under UNSC Res 1973(2011), UN Doc S/RES/1973 (2011), 17 March 2011; declaration available at Nonetheless, state practice is still limited and not entirely consistent in that regard.

15 There are so many references in state practice to the condition of proportionality as a specific requirement under the law of self-defence that it is impossible to mention all of these references here; see nn 26–28, 41 for references in particular cases.

16 See n 42.

17 Rome Statute of the International Criminal Court (entered into force 1 July 2002) 2187 UNTS 90 (‘ICC Statute’).

18 Emphasis added.

19 This may be supported by the fact that such a rule is not listed among the customary rules in the study on customary international humanitarian law sponsored by the International Committee of the Red Cross: Henckaerts Jean-Marie and Doswald-Beck Louise, Customary International Humanitarian Law, Vol I: Rules (ICRC, CUP 2005) (‘ICRC Study’).

20 See, for instance, Gardam Judith, Necessity, Proportionality and the Use of Force by States (CUP 2004) 15 (the author nonetheless concedes that ‘[t]echnically, it is more accurate today to talk in terms of superfluous injury or unnecessary suffering in the context of combatants, rather than proportionality’); see also David (n 7) 268; Greenwood Christopher, ‘Historical Developments and Legal Basis’ in Fleck Dieter (ed), The Handbook of International Humanitarian Law (OUP 2008) 35.

21 For example, the Preamble to the Declaration Renouncing the Use, in Time of War, of Explosive Projectiles under 400 Grammes Weight (opened for signature 29 November 1868, entered into force 11 December 1868) (‘St Petersburg Declaration’) in Schindler Dietrich and Toman Jiří (eds), The Laws of Armed Conflicts (3rd revised and completed edn, Martinus Nijhoff 1988) 102; Hague Convention (IV) respecting the Laws and Customs of War on Land and its annex: Regulations concerning the Laws and Customs of War on Land (entered into force 26 January 1910) Martens Nouveau Recueil (ser 3) 461, art 23; Additional Protocol I (n 6) art 35(2).

22 For example, Meyrowitz Henri, ‘The Principle of Superfluous Injury or Unnecessary Suffering’ (1994) 34 International Review of the Red Cross 98, 109–10; Hamutal Esther Shamash, ‘How Much Is Too Much? An Examination of the Principle of Jus in Bello Proportionality’ (2005–6) 2 Israel Defense Forces Law Review 103; Brown Bernard L, ‘The Proportionality Principle in the Humanitarian Law of Warfare: Recent Efforts at Codification’ (1976–7) 10 Cornell International Law Journal 134; ICRC Study (n 19) 46.

23 See, for example, ICTY, Prosecutor v Gotovina and Others, Judgment, IT-06-90-T, Trial Chamber I, 15 April 2011, [1171]–[1172], [1183], [1191]; ICTY, Prosecutor v Galić, Judgment, IT-98-29-A, Appeals Chamber, 30 November 2006, [190].

24 See Additional Protocol I (n 6) arts 51(5)(b) and 57(2)(a)(iii); see also art 3(8)(c) of the Protocol on Prohibitions or Restrictions on the Use of Mines, Booby-Traps and Other Devices as amended on 3 May 1996 annexed to the Convention on Prohibitions or Restrictions on the Use of Certain Conventional Weapons which may be Deemed to be Excessively Injurious or to have Indiscriminate Effects (entered into force 3 December 1998) UN CCW/CONF.I/ 1. It is now commonly agreed that this proportionality requirement has gained the status of a customary norm and that it is applicable in both international and non-international armed conflicts; on this subject see, for example, ICRC Study (n 19) 46–50.

25 See, for instance, Cannizzaro Enzo, ‘Contextualizing Proportionality: Jus ad Bellum and Jus in Bello in the Lebanese War’ (2006) 88 International Review of the Red Cross 779, 780.

26 See, for instance, statements of Russia (UN Doc S/PV.5489, 14 July 2006, 7); Qatar (ibid 10 and UN Doc S/PV.5493, 21 July 2006, 14); China (UN Doc S/PV.5489, 14 July 2006, 11); Japan (ibid 12); United Kingdom (ibid 13); Congo (ibid); Tanzania (ibid); France (ibid 17 and UN Doc S/PV.5493 (Resumption 1), 21 July 2006, 11); Slovakia (UN Doc S/PV.5493, 21 July 2006, 19); Finland (UN Doc S/PV.5493 (Resumption 1), 21 July 2006, 16); Algeria (ibid 22); Australia (ibid 27); Djibouti (ibid 32); New Zealand (ibid 33); India (ibid 34); Chile (ibid 35); Canada (ibid 39); Guatemala (ibid 41).

27 See, for instance, statements of Greece (UN Doc S/PV.5489, 14 July 2006, 17 and UN Doc S/PV.5493 (Resumption 1), 21 July 2006, 3); Russia (ibid 2); Switzerland (ibid 18); Norway (ibid 23); Indonesia (ibid 25); Morocco (ibid 29); South Africa (ibid 43–44).

28 See, for instance, state reactions to military actions conducted by Israel in the past and, in particular, statements in relation to the 1966 Israeli intervention in Jordan of the United Kingdom (UN Doc S/PV.1320, 16 November 1966, 19), United States (ibid 20–21); the Netherlands (UN Doc S/PV.1323, 18 November 1966, 3) and Uganda (UN Doc S/PV.1327, 24 November 1966, 4); statements in relation to the Israeli intervention in Lebanon in February 1972 of France (UN Doc S/PV.1643, 26 February 1972, 12), Italy (ibid 13–14), Argentina (UN Doc S/PV.1644, 27–28 February 1972, 3) and Somalia (ibid 18); statements in relation to the Israeli intervention in Lebanon in June 1972 of Sudan (UN Doc S/PV.1648, 23 June 1972, 11); France (UN Doc S/PV.1650, 26 June 1972, 2) and Italy (ibid 11). See also statements in relation to the intervention of the United Kingdom in Yemen in 1964 of Iraq (UN Doc S/PV.1106, 2 April 1964, 14–15); the Ivory Coast (UN Doc S/PV.1108, 6 April 1964, 10) and Czechoslovakia (UN Doc S/PV.1110, 8 April 1964, 5).

29 Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion [1996] ICJ Rep 226, 245 [42] (‘Nuclear Weapons’).

30 See Moussa (n 7) 974–75 (emphasis added) who stresses that such interpretation (which she does not share) has been advanced in legal literature in support of the proposition that ‘any act [which] contravenes jus in bello cannot be considered a proportionate and reasonable measure of self-defence under jus ad bellum’; see, in this respect, de Hemptinne Jérome and d'Aspremont Jean, Droit International Humanitaire (Pedone 2012).

31 Annex to UNGA Res 56/83, 12 December 2001, 6: this Article provides that ‘[t]he wrongfulness of an act of a State is precluded if the act constitutes a lawful measure of self-defence taken in conformity with the Charter of the United Nations’.

32 See, for instance, de Hemptinne and d'Aspremont (n 30). Such interpretation is founded upon the ILC commentary on the aforementioned Article 21, which provides that ‘the term “lawful” implies that the action taken [in self-defence] respects those obligations of total restraint applicable in international armed conflicts, as well as compliance with the requirements of proportionality and of necessity inherent in the notion of self-defence’: Report of the International Law Commission on the Work of its 53rd Session, UN Doc A/56/10, 2001, 75 para 6.

33 See, for instance, Österdahl Inger, ‘Dangerous Liaison? The Disappearing Dichotomy between Jus ad Bellum and Jus in Bello’ (2010) 78 Nordic Journal of International Law 553, 565; Cannizzaro (n 25) 791–92.

34 This principle is explicitly mentioned in Additional Protocol I (n 6) art 35(1).

35 Greenwood Christopher, ‘Self-Defence and the Conduct of International Armed Conflict’ in Dinstein Yoram (ed) and Tabory Mala (associate ed), International Law at a Time of Perplexity: Essays in Honour of Shabtai Rosenne (Martinus Nijhoff 1989) 273.

36 See, concerning such a limit, Nuclear Weapons (n 29) 242, [30]. The considerations held by the Court in that respect are nevertheless confusing. Indeed, while discussing the question of the relationships between the right of self-defence and the obligation to protect the natural environment, the Court asserted that ‘[s]tates must take environmental considerations into account when assessing what is necessary and proportionate in the pursuit of legitimate military objectives’ (emphasis added). It continued by saying that ‘[r]espect for the environment is one of the elements that go to assessing whether an action is in conformity with the principles of necessity and proportionality’ (emphasis added). By previously using the notion of ‘military objectives’, the Court seems to have referred to jus in bello. Moreover, in order to support its view, the Court further mentioned a series of legal texts which were only concerned with international humanitarian law. Although the Court did not elaborate on the principles of proportionality and necessity that it mentioned and did not expressly link those principles to jus ad bellum rather than jus in bello, it remains that proportionality under jus in bello was only recognised at that time in relation to civilians and civilian objects and not in relation to the natural environment as such. For the proportionality requirement with respect to the natural environment, see Section 1, ‘Introduction’.

37 For example, Oil Platforms (Iran v US), Merits, Judgment, 6 November 2003 [2003] ICJ Rep 161 (‘Oil Platforms’), [74].

38 ibid [77].

39 For example, Military and Paramilitary Activities in and against Nicaragua (Nicaragua v US), Merits, Judgment, 27 June 1986 [1986] ICJ Rep 14 (‘Nicaragua’), [237].

40 For example, Kolb Robert, Réflexions de philosophie du droit international. Problèmes fondamentaux du droit international public: Théorie et philosophie du droit international (Bruylant 2003) 322.

41 Apart from Israel (see, for example, UN Doc SP/V.1461, 30 December 1968, 11), states usually adopt a quantitative conception of proportionality. State reactions to the 2006 Israeli intervention in Lebanon are a clear example thereof: see, for example, in this respect, statements of Russia (UN Doc S/PV.5489, 14 July 2006, 7); Argentina (ibid 9); Qatar (ibid 10); China (ibid 11); Japan (ibid 12); Congo (ibid 13); Tanzania (ibid 13); Denmark (ibid 15); Greece (ibid 17); France (ibid); Ghana (UN Doc S/PV.5493 (Resumption 1)), 21 July 2006, 8); Brazil (ibid 19); New Zealand (ibid 33).

42 See Nicaragua (n 39) [237]; Oil Platforms (n 37) [76]–[77]; Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v Uganda), Merits, Judgment, 19 December 2005 [2005] ICJ Rep 168, [147].

43 Most of the scholars who support such an understanding refer to the considerations held on this subject by the former ILC Special Rapporteur: Roberto Ago, Addendum – 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), 69, para 121.

44 See, for a more detailed view on this issue, van Steenberghe Raphaël, ‘Self-Defence in Response to Attacks by Non-State Actors in the Light of Recent State Practice: A Step Forward?’ (2010) 23 Leiden Journal of International Law 183, 205–06.

45 Corten Olivier, The Law against War: The Prohibition on the Use of Force in Contemporary International Law (Hart 2010) 489.

46 See, for example, Wilmshurst Elizabeth, ‘The Chatham House Principles of International Law on the Use of Force in Self-Defence’ (2006) 55 International and Comparative Law Quarterly 963, 969 para E; Akande Dapo, ‘Nuclear Weapons, Unclear Law? Deciphering the Nuclear Weapons Advisory Opinion of the International Court’ (1997) 68 British Yearbook of International Law 165, 191; Moussa (n 7) 978; Cannizzaro (n 25) 786.

47 Gardam (n 20) 19.

48 See, for instance, on the subject Steenberghe Raphaël van, La légitime défense en droit international public: Statut, contenu et preuve (forthcoming, Larcier 2012) 273343.

49 See n 24.

50 Emphasis added. The currently debated question of whether the term ‘military advantage’ refers to the advantage anticipated from the attack as a whole or only from the isolated or specific elements thereof is a distinct issue (see, for instance, in this respect, ICRC Study (n 19) 49–50 and the state declarations mentioned by these authors). In any event, the notion of ‘attack as a whole’ is not used as meaning the whole military campaign that may be conducted in self-defence but rather as referring at best to a series of military actions which are part of the individual attack launched in the framework of such a campaign. See, in this respect, fn 36 in the ICC Elements of Crimes (entered into force 9 September 2002) ICC-ASP/1/3 (Part II-B): although the term ‘overall’ was added before the notion of ‘military advantage’, in art 8(2)(b)(iv) of the ICC Statute, the explanatory footnote states that ‘[t]he expression “concrete and direct overall military advantage” refers to a military advantage that is foreseeable by the perpetrator at the relevant time. Such advantage may or may not be temporally or geographically related to the object of the attack. (…) It does not address justifications for war or other rules related to jus ad bellum. It reflects the proportionality requirement inherent in determining the legality of any military activity undertaken in the context of an armed conflict’.

51 See n 25.

52 As one author, commenting on the Israeli intervention in Lebanon in 2006, has validly argued, ‘a defensive military campaign might not be out of proportion to the attack defended against (a jus ad bellum issue), but some of the tactics used in the campaign might contravene the jus in bello if the risk to civilians or to civilian objects is disproportionate to the military advantage to be gained by using those tactics’: Frederic L Kirgis, ‘Some Proportionality Issues Raised by Israel's Use of Armed Force in Lebanon’, 17 August 2006, available at

53 See Orakhelashvili (n 9) 163, who asserts that ‘jus in bello and jus ad bellum contain separate but cumulative requirements’.

54 Moussa (n 7) 975.

55 Österdahl (n 33) 565.

56 See, for example, Greenwood (n 35) 278.

57 Cannizzaro (n 25) 785.

58 Gardam (n 20) 17.

59 Meron Theodor, ‘The Humanization of Humanitarian Law’ (2000) 94 American Journal of International Law 239, 241.

60 See, for example, Friedhelm Krüger-Sprengel, ‘Le concept de proportionnalité dans le droit de la guerre’ (Rapport présenté au Comité Pour la Protection de la Vie Humaine dans les Conflits Armés, VIIIe Congrès de la Société Internationale de Droit Pénal Militaire et de Droit de la Guerre), (1980) 19 Revue de Droit Pénal Militaire et de Droit de la Guerre 177, 181.

61 Gardam Judith, ‘Proportionality as a Restraint on the Use of Force’ (1999) 20 Australian Yearbook of International Law 161, 168.

62 The fact that the military operation entails only one or a few forcible measures does not necessarily imply that jus in bello is not applicable in that case. It is indeed well supported in legal literature that violence must not reach any particular level of intensity in order for humanitarian law to be applicable when this violence breaks out between two states (see, for instance, Pictet Jean, Commentary on the Geneva Convention I (ICRC 1952) 34; Kolb (n 2) 158). Although such a level of intensity may be required in case of a conflict occurring in the territory of a state between the military forces of another state and non-state actors such as terrorists (see the US Supreme Court which qualifies the conflict between the US Army and Al Qaeda in Afghanistan as a non-international armed conflict (Hamdan v Rumsfeld (2006) 45 International Legal Materials 1154)), the possible limited action by the state acting in self-defence abroad could be a response to a series of attacks by the non-state actors, which, taken cumulatively, evidence a high level of violence. This would make jus in bello applicable.

63 See, for examples of such situations in addition to those mentioned below, the US military bombings in Afghanistan in 1998: Letter from the Permanent Representative of the United States of America to the United Nations addressed to the President of the Security Council, UN Doc S/1998/780, 20 August 1998.

64 n 37.

65 See the oral pleadings by Iran, public sitting in the case concerning Oil Platforms, 19 February 2003, CR 2003/7, para 63.

66 See the oral pleadings by the United States, public sitting in the case concerning Oil Platforms, 26 February 2003, CR 2003/12, para 18.32.

67 Legal Consequences of the Construction of a Wall in the Occupied Palestinian Territory, Advisory Opinion [2004] ICJ Rep 136 (‘Wall Advisory Opinion’), [138].

68 ibid [139].

69 ibid, Separate Opinion of Judge Kooijmans, [34].

70 ibid, Separate Opinion of Judge Higgins, [35].

71 See, for example, written statements of France, paras 57–58, available at, and South Africa, para 36, available at

72 See, for example, written statement of Saudi Arabia, para 34, available at

73 See, for example, written statements of Indonesia, para 7, available at, and Malaysia, para 151, available at

74 Nuclear Weapons (n 29) 266, dispositive, E.

75 ibid.

76 See, for example, Lanfranchi Marie-Pierre and Christakis Théodore, La licéité de l'emploi d'armes nucléaires devant la Cour Internationale de Justice (Economica 1997) 108.

77 See, for example, Nuclear Weapons (n 29), Separate Opinion of Judge Koroma, 559–60; Separate Opinion of Judge Fleischhauer, ibid 308 [5].

78 See, for instance, Dissenting Opinion of Judge Ranjeva (ibid 301); Dissenting Opinion of Judge Higgins (ibid 590 [29]); Dissenting Opinion of Judge Shahabuddeen (ibid 426).

79 n 77.

80 ibid.

81 Nuclear Weapons (n 29).

82 ibid, Dissenting Opinion of Judge Higgins, [25].

83 ibid [21].

84 Österdahl (n 33) 565.

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