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Gardam, Judith --- "Proportionality as a Restraint on the Use of Force" [1999] AUYrBkIntLaw 9; (1999) 20 Australian Year Book of International Law 161

Proportionality as a Restraint
on the Use of Force

Judith Gardam[∗]


Professor Don Greig is one of the few scholars to address the issue of proportionality in treaty making.[1] In doing so Greig draws on a life-time’s acquired expertise in contract in both the municipal and international law setting. The concept of proportionality has been part of municipal and international law for centuries.[2] As Greig writes: ‘the balancing of interests is fundamental to the role of the law in promoting the well-being of society and proportionality has played its role in this process’.[3]

For some writers, proportionality constitutes a general principle of law.[4] For others, it is doubtful whether it has attained this status.[5] Rosalyn Higgins, citing its role in maritime delimitation, the use of force and human rights law, sees proportionality as a concept to ‘ease’ the ‘appropriate application’ of norms of international law in ‘particular cases’.[6] Other writers prefer to characterise proportionality as deriving its legitimacy from natural law.[7]

Nowadays, proportionality is part of the legal regime of both ius ad bellum and ius in bello, or international humanitarian law (IHL) as it is more commonly known. In the former it determines the limits on a belligerent’s overall response to a grievance and, in the latter it determines the balance to be struck between the achievement of a military goal and the cost in terms of lives.[8] The fact that proportionality operates today in these two different systems has led to some intractable problems about the relationship between its two aspects, a phenomenon illustrated by the Advisory Opinion of the International Court of Justice in the Legality of the Threat or Use of Nuclear Weapons.[9]

The role of proportionality in regulating forceful actions of states has varied over the years. During the developmental stages of the current system it is probably best seen as a guiding principle with little specific content. Over the years, however, proportionality has become a sophisticated concept with a wide operation. For example, it is regarded as one of the fundamental principles on which the whole of modern IHL is based. From it are derived some of the specific rules of IHL.[10] In other situations, proportionality has developed into a concrete legal norm itself, for example, as one of the requirements of legitimate self-defence under the United Nations (UN) system and the treaty rule of proportionality in Article 51(5)(b) of Protocol I.[11] This article addresses the development and content of proportionality in ius ad bellum and ius in bello and assesses state practice in recent international armed conflicts to determine whether proportionality is performing its role as a general restraint on force.

The Development of Proportionality

An understanding of the development and role of proportionality requires an appreciation of the relationship between ius ad bellum and ius in bello.[12] The connection between the two doctrines generally is complex and is rarely clearly articulated.[13] The division between the two systems is relatively recent. Until the nineteenth century there was no separate ius in bello. Any limitations on the conduct of warfare were originally to be found in the general theory of the just war. There are many just war theories as most civilisations have had highly developed rules relating to the justness of the resort to war.[14] However, the Christian theory of the just war formed the basis of the secular just war writings of commentators such as Grotius and Vattel.[15] This theory is a complex interplay of various religious, moral and secular factors. In just war theory, proportionality limited the amount of damage that could be legitimately inflicted on an enemy. It was a requirement of a just war that the overall evil of the war was balanced by the overall good; a just war, ipso facto, was a proportional one. However, in reality proportionality was a relatively vague notion and it is doubtful that it ever was a restraining influence on the resort to or conduct of war.[16] Theoretically, proportionality in those times encompassed a consideration of such matters as legitimate weapons, enemy casualties and damage to enemy property. The concept of proportionality that pertained at that time combined aspects of what is now found in two separate systems, ius ad bellum and ius in bello.

The period after the demise of the just war saw the development of the idea that the resort to force was a sovereign right of states. It was during this time that ius in bello commenced its separate development. However, proportionality in its modern ius ad bellum aspect, that is, as limiting a state’s overall forceful response, did not fall into disuse. It is not surprising that states saw some mutual benefit in limiting the impact of war, even if at the time they saw no advantage to restricting the right to wage war. Thus, it was during the period when war was a right of states that the developing rules of ius in bello performed to some extent the function of proportionality that is now the province of ius ad bellum. Today, proportionality in ius in bello is somewhat narrowly defined in relation to an attack, or a series of attacks, or the use of particular weapons causing unnecessary suffering or superfluous injury; the broader issue of how those attacks relate to the aims of the use of force, is part of ius ad bellum. However, during the period when war was viewed as a sovereign right of states, the limitations flowing from considerations of proportionality were sometimes expressed in broad terms so as to take into account not only the use of particular weapons against combatants (and to a very limited extent the question of civilian casualties) but also overall disproportionate warfare.

Proportionality in the Charter Era

In modern international law there is a clear distinction between the law regulating the resort to force and IHL. The legitimate resort to force under the UN system is regarded by most commentators as restricted to the use of force in self-defence under Article 51 and collective security action under Chapter VII of the UN Charter.[17] There is, however, intense debate about such issues as the extent of the right of self-defence under Article 51, the effect of the Charter on the pre-existing customary right of self-defence, particularly the right of preventative self-defence, and the relationship between legitimate self-defence and unlawful reprisals. In recent times the use of force in the context of humanitarian intervention has been at the forefront of developments.[18]

Nevertheless, proportionality is a remarkably consistent theme running throughout discussions on the use of force. Despite wide differences expressed by commentators and as evidenced in the practice of states, as to when the resort to force is legitimate in international law, there is unanimous agreement on the need for the forceful action to be proportionate. For example, Rosalyn Higgins, in the context of preventative action against state supported border raids by irregulars, writes that force may legitimately be used in such a situation ‘but always with the proviso that the action in self-defence is proportionate, in nature and degree to the prior illegality or the imminent attack’.[19] A similar view is articulated in the context of humanitarian intervention both unilateral and collective.[20] The answer to the question ‘proportionate to what?’, however, is far from uniform. Derek Bowett, on the one hand, like Higgins, claims that the response must be proportionate to the danger.[21] Sir Humphrey Waldock, on the other hand, writes in terms of what is ‘required for achieving the object’.[22]

Modern IHL limits the effects of warfare for both combatants and civilians. The concept of proportionality, along with restraints derived from humanity and chivalry, plays a pivotal role in this process. It is part of the ‘Law of The Hague’ which deals with the conduct of warfare. The rules derived from the principle that armed conflict should not be conducted in a disproportionate manner take different forms in relation to combatants and civilians. Combatants are legitimate targets in armed conflict. Civilians are not. Combatants today are protected by the prohibition of means and methods of warfare that are of a nature to cause unnecessary suffering or superfluous injury.[23] In the context of civilians, the development of proportionality is linked with the growth over the centuries of the idea that civilians should be protected from the effects of warfare. By the beginning of last century it was accepted in a general sense that civilians were not legitimate objects of attack.[24] However, this limitation was inadequate to deal with the growing impact of armed conflicts on civilians, particularly in the light of the development of means and methods of warfare that inevitably resulted in civilian casualties. In current international law, it is the concept of proportionality that has assumed the pivotal role in determining the extent to which civilians are entitled to be protected from the collateral effects of armed conflict.[25]

Since the adoption in of Protocol I 1977, the requirement that attacks do not result in disproportionate civilian casualties is both a conventional and customary rule of IHL.[26] The prohibition on means and methods of warfare that cause unnecessary suffering or superfluous injury, limits the effects of warfare on combatants, and for many years has enjoyed customary and conventional status.[27]

The use of the term proportionality in relation to the rules that regulate the means and methods of warfare for the protection of combatants has been criticised.[28] Technically it is more accurate today to talk in terms of unnecessary suffering in the context of combatants rather than proportionality.[29] The principle that prohibits the infliction of unnecessary suffering on combatants and the modern rule of proportionality in relation to civilians, however, have a common origin and goal, to minimise the torment caused by war — to ensure that the suffering and loss of life of both civilian and combatant are not disproportionate to the legitimate ends. They find a common source in the foundation principle of IHL that belligerents do not have unlimited choice in the means chosen to inflict damage on the enemy. Although strictly speaking, this latter principle was developed with combatants in mind, it provided the basis for the movement that coalesced after the Second World War, to place real limits on the impact of warfare on civilians. Proportionality, therefore, is not only the specific rule expressed in Protocol I in relation to civilians, it is a general principle that underlines several of the rules of IHL.

The rationale behind proportionality in the two regimes differs. The limitations imposed by proportionality in ius ad bellum relate to the minimisation of the disruption of international peace and security.[30] Thus the argument in the context of self-defence, is that proportionality ensures that states are allowed the minimum that is required to defend themselves against an aggressor. To go any further and allow excessive destruction of another state is seen as destabilising a system that is founded on the peaceful settlement of disputes and a collective security system. Consequently, the major considerations in the application of proportionality in modern ius ad bellum, be it in the context of self-defence or any other ground on which the use of force is argued to be legitimate, are as follows: first, overall combatant and civilian casualties; second, the level of destruction of enemy property; and third, the impact of the use of force on third states (with a developing emphasis in the latter context on damage to the environment).

Moreover, in recent times, it appears that considerations of humanity also influence what states regard as proportional measures in self-defence. This development is attributable to the growing emphasis on human rights and an increasing awareness of the haphazard impact of the boundaries of human rights law, ius ad bellum and ius in bello. The operation of these factors can be seen in the Persian Gulf conflict in 1990–91. More destruction was perhaps regarded as legitimate in that conflict than may have otherwise been the case, in light of the clear-cut nature of Iraq’s aggression and the collective nature of the response. However, as the campaign of the Coalition allies inflicted escalating levels of damage on Iraq and its population, the continuing support of neighbouring Arab states and the international community generally became increasingly problematic.

The general view is that provisions in IHL derived from proportionality that limit the level of damage to civilians and combatants are based on humanitarian considerations.[31] The emphasis on humanity is a relatively late development. Its influence generally in ius in bello is controversial and it would be simplistic to see the foundations of the system as purely humanitarian. Humanity has undoubtedly played a significant role in the development of ius in bello (particularly in the context of what is known as Geneva Law) and is of increasing importance given the growing emphasis on human rights. The notion that the needless suffering of combatants and high levels of civilian casualties are unacceptable in warfare, was largely unknown until the growth of humanism in the eighteenth century. During the period of the just war, the extent to which humanity played any significant role in the regulation of warfare is debatable. The proportionality equation was intimately connected with Christian ideas of good and evil, intermingled with secular influences.

Today, the issue is no less complex. At a superficial level ius in bello is widely acknowledged as being based on humanitarian considerations. This explains the changing nomenclature of this area of the law.[32] To some commentators, however, the term IHL disguises the reality particularly in the context of the rules regulating the conduct of armed conflict, such as proportionality. A study of IHL reveals that developments in the protections offered to all victims of armed conflict, both combatants and non-combatants, have been in spite of the military rather than at its instigation. Some restrictions in rules protecting combatants have been tolerated, such as weapons causing unnecessary suffering, and the extremely detailed provisions protecting prisoners of war.[33] These rules may appear humanitarian in nature but they also are consistent with military considerations.[34] By contrast, there is no obvious military advantage to be gained in protecting civilians. In the development of IHL, humanitarian considerations have always taken second place to a plea of military necessity, especially when the proposed changes are to improve the protection offered to non-combatants.

Despite the appalling suffering of civilians in armed conflict from the development last century of weapons of mass destruction, it was not until the influence of human rights began to make its impact on IHL that steps were taken to improve the protection offered to civilians by IHL. These advances were hard-won in the face of much opposition from the military establishment of states. The emergence of the prohibition on disproportionate civilian casualties as a treaty and customary rule is an outstanding example of what can be accomplished. The extent of the achievement is illustrated by the criticisms the treaty rule has attracted from military commentators.[35] However, the actual application of these rules in subsequent conflicts has been disappointing. In the context of combatants, there is broad-based support for the view that humanitarian considerations have led to little real progress in improving their protection against means and methods of warfare causing unnecessary suffering.[36]

The influence of humanity, to some extent, explains why ius in bello as a whole and proportionality in particular deals with individuals in a way that proportionality in ius ad bellum does not. The latter has always focused on damage to the enemy state as an abstract entity apart from its individual inhabitants, by taking into account such factors as infringement of territorial sovereignty and the general destruction caused to the state and its population. Today the dual proportionality equations incorporate a consideration of the same general factors but with a different emphasis. So weapons are relevant for proportionality in ius in bello and ius ad bellum. But in the former it is the effect of a weapon on civilians and combatants as individuals that requires assessment. In the latter, the relevant factors when considering whether a particular weapon or its use is a proportionate action in self-defence relate to damage to the civilian population as a whole, the level of destruction of the enemy forces, and finally damage to territory, the infrastructure and the environment.

The distinction between ius ad bellum and ius in bello is also significant in terms of the consequences of a failure to comply with their requirements. On the one hand, for example, a disproportionate action under IHL or the use of means and methods of warfare that cause unnecessary suffering or superfluous injury to combatants, is not only a breach of those rules (and in some cases a grave breach of the treaty rule)[37] but also does not qualify as a legitimate action in self-defence. On the other hand, meticulous compliance with the proportionality requirements of IHL will not prevent an action being disproportionate under ius ad bellum.[38]

The legal regime of proportionality in international law is criticised by scholars from other disciplines. There are undoubtedly limitations in the modern legal doctrine. The complex equation of the just war theory of proportionality, as to whether the overall costs of the war outnumber the benefits, is not mirrored in the requirements of international law.[39] Proportionality in earlier Christian and secular just war theories purported to be a restraint on the resort to force, not just the conduct of force, as is the case with proportionality today. It is the narrow scope of proportionality in international law that forms the basis for its criticism by just war scholars. In their view it is a doctrine that merely limits the means and takes no account of the wider issues of whether the overall good balances the overall evil of the use of force. Or to put it crudely, the assessment of proportionality in international law is confined to the counting of bodies.[40] It can be argued that to transpose the complexity and overt subjectivity of the balancing process in just war theory into a legal regime is unworkable.[41] Moreover, to some extent states have lessened the circumstances that can give rise to the need for such an assessment by establishing a legal regime where the overall disadvantages of the unilateral resort to force always outweigh the benefits except in cases of self-defence. Proportionality then determines that this right is exercised in a manner that is commensurate with the aims of self-defence.

The question of the overall ‘good’ of the use of force in contexts other than self-defence is left to the Security Council. The Security Council’s mandate is to take whatever action it determines appropriate to restore international peace and security. A broad assessment of the overall advantages as opposed to the disadvantages of the use of force is part of such an analysis. It seems, therefore, that proportionality in the broader sense of being a factor in determining not only the conduct of force but the initial decision to use force, is inherent in the role of the Security Council. Such a process, however, is primarily political rather than legal.

Proportionality in the post-Cold War era

Although it is somewhat doubtful as to whether at any stage the requirements of proportionality were of real significance in practice in either ius ad bellum or ius in bello, developments since the end of the Cold War, particularly the events of the Persian Gulf conflict and the 1999 Kosovo conflict have further eroded their significance.[42] An examination of the recent practice of states confirms that proportionality in the context of ius ad bellum primarily serves as a rhetorical tool to support whatever view is taken as to the morality of a particular use of force.[43] Its requirements are rarely clearly articulated and its constraining role is questionable. Although proportionality in IHL has moved from what Greig describes as a general proposition to a ‘variety of rules’, even with this precision, the effectiveness of its restraints remains debatable.[44]

The Persian Gulf conflict is a particularly useful case study of proportionality as it was a large-scale international armed conflict involving many states. Moreover, there was vigorous debate over the legality of the use of force by the Coalition forces in that conflict, from the perspective of whether the use of force was an exercise in collective self-defence or was authorised by the Security Council.[45] This is an important question as the characterisation of the resort to force determines the role of proportionality. Put simply, in the context of the Persian Gulf conflict, a collective security action required an evaluation of whether the means employed were proportionate to achieving the goal of restoring international peace and security, whereas an action in collective self-defence involved an evaluation of the response in terms of the removal of Iraq from Kuwait. Consequently, the Persian Gulf conflict involved a consideration of the operation of proportionality in the context of self-defence and in the exercise of the enforcement powers of the Security Council.

Despite the considerable differences as to the applicable law and its implementation, there was consistent support from states that proportionality was relevant in the decision-making processes involving the use of force in the Persian Gulf conflict. Although difficult to establish, given the complex interplay of political, military and legal considerations that characterised this conflict, it is arguable that overall this principle played some role in limiting the forceful actions of the states involved. Considerations of proportionality were factors (amongst many others of a military and political nature) in the decision to stop short of overthrowing of the regime of Saddam Hussein and destroying the military capability of Iraq.[46] The requirements of proportionality in IHL were also relevant in the actual conduct of the campaign. In the context of civilian casualties, there was little evidence to indicate disproportionate attacks.[47] Nonetheless, despite lip service to the requirements of proportionality in both ius ad bellum and IHL, the extension of the campaign beyond the borders of Kuwait into Iraq and the effects of the campaign of aerial bombardment on the infrastructure of a highly developed state, resulted in widespread immediate and long-term civilian casualties (not to mention considerable Iraqi combatant casualties).[48]

Part of the explanation for the seeming inability of the requirements of proportionality to prevent extensive ‘collateral’ damage to civilian and civilian objects is attributable to the recent practice of states of prioritising the protection of their own combatants. This phenomenon has increasingly eroded the potential of proportionality to perform its task of protecting civilians. The prioritising of combatants lives in ‘morally’ (if not always legally) justifiable resorts to force can be seen not only in the Persian Gulf conflict but also the ‘zero casualties’ policy of the NATO forces in the 1999 Kosovo conflict.[49] The proportionality equation, as it currently stands in IHL, does not deal with the extent to which a military commander must assume a higher level of risks for his/her own combatants in order to protect the civilian population of the opposing side.[50] This issue is relevant in decision-making as to the choice of weapons, the method of attack and the verification of targets.[51] For example, aerial bombardment at high-level altitudes may minimise combatant casualties but leads to increased risk of civilian casualties and widespread damage to civilian objects.

The failure of IHL to regulate policies that aim to minimise a state’s own combatant casualties is exacerbated by the fact that the proportionality equation in ius ad bellum that could perform this function in reality does not do so. It appears that a state is also at liberty to plan its campaign, including its preferred method of warfare, in order to reduce its combatant casualties without infringing the requirements of ius ad bellum.

Another shortcoming of the legal regime of proportionality, particularly in relation to overall civilian losses, is that it appears that in a determination of whether a particular response is proportionate under both ius ad bellum and IHL, only direct civilian casualties are taken into account. As the Persian Gulf conflict indicates, long-term civilian casualties resulting from starvation and disease do not appear to be part of the equation. Neither is the extent to which any forceful action will lead to the displacement of the civilian population and the creation of large numbers of refugees.[52]


Currently, if one relies on what states say and the reflections of commentators, proportionality in the context of forceful actions of states appears to be undergoing somewhat of a renaissance and, moreover, assuming a broader role. There are indications of an emerging doctrine of proportionality that will perform the function of ensuring the protection of human rights and humanitarian values in all forms of coercion: unilateral and collective countermeasures, self-defence and the enforcement powers of the Security Council. One of the early indications of this phenomenon can be discerned in the third and fourth reports of the International Law Commission on State Responsibility in the context of unilateral countermeasures.[53] Increasingly, references to such humanitarian values are being expressed as a component of proportionality, whereas, traditionally, in the context of countermeasures and self-defence, proportionality was based on other considerations.

However, when one balances the results of the forceful actions of states in recent conflicts it appears that proportionality has a long way to go before it will perform its alleged role in acting as a general restraint on force. It can be argued that the concept in the context of ius ad bellum is too difficult to apply in practice, given the nature of the activity that it is attempting to regulate. However, it is at the stage of determining what is proportionate to achieving the overall aim of the use of force that the most can be achieved for the protection of the civilian population. The detailed application of the rule at the IHL level only deals with the ‘small picture’. It is ius ad bellum that controls the legitimacy of the choice of methods of warfare, such as high-altitude aerial bombardment. Although the legality in ius ad bellum terms of both the Persian Gulf and Kosovo conflicts were assessed in considerable detail, scant attention was paid to whether they were proportionate.

It is apparent that once states decide that their political agendas require forceful actions, the Charter rules will not deter them. However, it is to be hoped that the increasing recognition of the importance of respecting human rights might lead in the future to a re-consideration of what is acceptable in the pursuit of these agendas, in terms of the overall price paid in short- and long-term damage to the civilian population and civilian objects for such actions.


Case Concerning the Gabčikovo-Nagymaros Project (Hungary v Slovakia) [1997] ICJ Rep 3 1

Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep 26 2


United Nations Charter 1945 4, 13

[∗] Associate Professor of Law, University of Adelaide.

[1] See D W Greig, ‘Reciprocity, Proportionality, and the Law of Treaties’ (1994) 34 Virginia Law Review 295.

[2] See ibid 295–298. Proportionality is familiar to international lawyers as a requirement of legitimate countermeasures. See art 49 of the Draft Articles on State Responsibility adopted provisionally on first reading by the International Law Commission at its 48th sess 1996, Report of the International Law Commission on the work of the 48th sess, UN GAOR (51st sess), Supp No 10, 25, UN Doc A/51/10 (1996) and Third Report on State Responsibility, International Law Commission, 43rd sess, UN Doc A/CN.4/440/Add1 (1991) 63–68 (report by Gaetano Arangio-Ruiz). See also Case Concerning the Gabčikovo-Nagymaros Project (Hungary v Slovakia) [1997] ICJ Rep 3 where the test of proportionality is articulated as ‘the effects of a countermeasure must be commensurate with the injury suffered, taking account of the rights in question’. See also J G Gardam, ‘Proportionality and Force in International Law’ (1993) 87 American Journal of International Law 391.

[3] See Greig, above n 1.

[4] See, eg, J Delbruck, ‘Proportionality’ in R Bernhardt (ed), The Encyclopedia of International Law (1981–91) 1144; and F 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, Ankara, Octobre 1979, 194: ‘elle [proportionnalité] est un principe général dont il, faut tenir compte dans l’interprétation des règles pertinentes du droit international’.

[5] See, eg, R Higgins, Problems and Process: International Law and How We Use It (1994) 236.

[6] Ibid 228–235; and see also above n 1.

[7] See M Reisman and D Stevick, ‘The Applicability of International Law Standards to United Nations Economic Sanctions Programmes’ (1998) 9 European Journal of International Law 86, 129.

[8] A Roberts and R Guelff, Documents on the Law of War (2nd ed, 1989) 5. See also M McDougal and F Feliciano, Law and Minimum World Public Order: The Legal Regulation of International Coercion (1961) 528, 241–244 for their definition of proportionality in ius ad bellum; and W O’Brien, The Conduct of Just and Limited War (1981) 27–31.

[9] Legality of the Threat or Use of Nuclear Weapons (Advisory Opinion) [1996] ICJ Rep 26. The Court was confronted in that case with determining the legality of a weapon that seemingly was totally incompatible with the requirements of IHL but was nevertheless an integral component of the defensive strategies of a significant number of states. The demands of the ius ad bellum prevailed. See also J Gardam, ‘Necessity and Proportionality in Jus ad Bellum and Jus in Bello’ in L Boisson de Chazournes and P Sands (eds), International Law, the International Court of Justice and Nuclear Weapons (1999) 275 and C Greenwood, ‘Jus ad Bellum and Jus in Bello in the Nuclear Weapons Advisory Opinion’ in de Chazournes and Sands, ibid 247.

[10] Eg, the emerging protections for the environment in IHL are based on considerations of proportionality. See art 35(3) of Protocol I (see below n 11) which prohibits the employment of ‘methods or means of warfare which are intended, or may be expected, to cause widespread, long-term and severe damage to the natural environment.’

[11] Protocol Additional to the Geneva Conventions of 12 August 1949, and relating to the Protection of Victims of International Armed Conflicts, adopted in 1977 (Protocol I) [hereinafter Protocol I] 1125 UNTS (1979) 3.

[12] The terms ius in bello and ius ad bellum are of recent coinage although used to describe developments that occurred over many centuries. See R Kolb, ‘Origin of the Twin Terms Jus ad Bellum and Jus in Bello(1997) 320 International Review of the Red Cross 553.

[13] See, however, the careful analysis by C Greenwood in ‘The Relationship between Ius ad Bellum and Ius in Bello’ (1983) 9 Review of International Studies 221.

[14] See, eg, M Sornarajah, ‘An Overview of the Asian Approaches to International Humanitarian Law’ [1980] AUYrBkIntLaw 48; (1985) 9 Aust YBIL 238.

[15] See H Grotius, ‘De Jure Belli ac Pacis Libri Tres’ in J Scott (ed), The Classics of International Law (F Kelsey trans, 1925) vol 2(3); and E de Vattel, ‘Le Droit de Gens, ou Principes de la Loi Naturelle, Appliqués à la Conduite et aux Affaires des Nations et des Souverains’ in J Scott (ed), The Classics of International Law (C Fenwick trans, 1916) vol 3, 305 [190]. There are a number of excellent works on the historical development of the Christian theory of the just war and on the modern form of this theory, see, eg, J Johnson, Ideology, Reason and the Limitation of War (1975); F Russell, The Just War in the Middle Ages (1975); and M Walzer, Just and Unjust Wars (2nd ed, 1991). The just war and international law has also received attention from legal scholars: see, eg, O’Brien, above n 8.

[16] See Gardam, above n 2, 394–6.

[17] See O Schachter, International Law in Theory and Practice (1991) 106.

[18] Eg, in the context of the NATO action in Kosovo 1999, see B Simma, ‘NATO, the UN and the Use of Force, Legal Aspects’ (1999) 10 European Journal of International Law 1; A Cassese, ‘Ex Injuria Ius Oritur: Are We Moving Towards International Legitimation of Forcible Humanitarian Countermeasures in the World Community?’ (1999) 10 European Journal of International Law 23; and A Cassese, ‘A Follow Up: Humanitarian Countermeasures and Opinio Necessitatis(1999) 10 European Journal of International Law 791.

[19] R Higgins, The Development of International Law Through the Political Organs of the United Nations (1963) 201. See also H Waldock, ‘The Regulation of the Use of Force by Individual States in International Law’ (1952) 81 Recueil des Cours 455, 463–4.

[20] See, eg, C Chinkin, ‘Kosovo: A Good or Bad War?’ (1999) 93 American Journal of International Law 841, 844–5; J Charney, ‘Anticipatory Humanitarian Intervention in Kosovo’ (1999) 93 American Journal of International Law 834, 839; Casesse, above n 18, 27; and V Nanda, ‘The Validity of United States Intervention in Panama under International Law’ (1990) 84 American Journal of International Law 494, 496.

[21] D Bowett, Self-defence in International Law (1958) 269.

[22] Waldock, above n 19, 463–4.

[23] See, eg, S Oetner, ‘Methods and Means of Combat’ in D Fleck (ed), Handbook of Humanitarian Law in Armed Conflict (1995) 105–153.

[24] See J Gardam, Non-Combatant Immunity as a Norm of International Humanitarian Law (1993) 16–20; and G Best, War and Law Since 1945 (1994) 26–44.

[25] See Roberts and Guelff, above n 8, fn 2.

[26] See arts 51(5)(b) and 57(2)(a)(iii) of Protocol I which encapsulate the concept of proportionality. The exact content of the customary rule is, however, controversial.

[27] See F Hampson, ‘Means and Methods of Warfare in the Conflict in the Gulf’ in P Rowe (ed), The Gulf War 199091 in International and English Law (1993) 89, 101.

[28] See H Meyrowitz, ‘The Principle of Superfluous Injury or Unnecessary Suffering’ (1994) 299 International Review of the Red Cross 98, 109–10.

[29] Commentators constantly use the word ‘proportionate’ in relation to the regulation of weapons to protect combatants. See, eg, above n 23, 114 [402]; and A Cassese, ‘Weapons Causing Unnecessary Suffering: Are They Prohibited?’ (1975) 48 Rivista di Diretto Internazionale 12, 27–9.

[30] See C Greenwood, ‘Self-defence and the Conduct of International Armed Conflict’ in Y Dinstein (ed), International Law at a Time of Perplexity: Essays in Honour of Shabtai Rosenne (1989) 273, 278.

[31] See Krüger-Sprengel, above n 4, 181.

[32] See J Gardam (ed), Humanitarian Law (1999).

[33] The Third Geneva Convention, in relation to prisoners of war, has some 143 Articles and five Annexes and goes to the lengths of stipulating what should be available in the prison canteen. For a study of the long and complex history of the rules protecting prisoners of war, see generally A Rosas, The Legal Status of Prisoners of War (1976).

[34] See C af Jochnick and R Normand, ‘The Legitimation of Violence: A Critical History of the Laws of War’ (1994) 35 Harvard International Law Journal 49, 53–4, 68. Cf a traditional description of the humanitarian ideal underlying the law of armed conflict and its relationship with military necessity by G Draper, ‘The Development of International Humanitarian Law’ in International Dimensions of Humanitarian Law (1988) 67.

[35] See, eg, W Hays Parks, ‘Air War and the Law of War’ (1990) 32 Air Force Law Review 1.

[36] See L Doswald-Beck, ‘Obstacles to Regulating New Weaponry: Battlefield Laser Weapons’ in H Fox and M Meyer (eds), Effecting Compliance, Armed Conflict and the New Law (1993) 107; and af Jochnick and Normand, above n 34.

[37] See, eg, art 85(3)(b) of Protocol I.

[38] See generally F Kalshoven, ‘State Responsibility for Warlike Acts of the Armed Forces’ (1991) 40 International and Comparative Law Quarterly 827.

[39] R Tucker, The Just War: A Study in Contemporary American Doctrine (1960) 128–9, fn 16 describes the just war concept as follows: ‘[t]he latter [the bellum justum doctrine] requires that the evil imposed by war be outweighed by the good sought on the part of those who have a just cause and are inspired by the ‘right intent’, the intent to maintain justice in the interest of the common good’.

[40] See, eg, R Osgood and R Tucker, Force, Order and Justice (1967) 300–301 and M Walzer, above n 15, xv–xvii.

[41] See R Tucker, above n 39, 128–9, fn 16.

[42] O Schachter in the context of ius ad bellum, regards this question as ‘one of the most sensitive subjects of contemporary international law … [i]n virtually all wars, questions of necessity and proportionality have given rise to controversy that is troubling and divisive’. He concludes that the existence of these legal principles, although incapable of providing a straightforward answer to concrete situations, nevertheless act as a general restraint on decision makers and that is their value. See ‘Implementing Limitations on the Use of Force: The Doctrine of Proportionality and Necessity’ in D Alexander (ed), ‘Contemporary International Law Issues, Sharing Pan-European and American Perspectives: Proceedings of the Joint Conference held in The Hague, The Netherlands, 4–6 July 1991’ (1992) 39.

[43] Cf the conclusions reached as to the legality of the forceful actions of NATO in Kosovo by Chinkin, above n 20, 844–5; and M Reisman, ‘Kosovo’s Antinomies’ (1999) 93 American Journal of International Law 860, 861–2. Both authors refer to proportionality to support their views. Chinkin, however, transcends rhetoric and provides an analysis of the factors that she regards as part of the proportionality equation that were not satisfied by NATO’s response in Kosovo. See also above n 7, 129.

[44] See Greig, above n 1, 298 and also P Rowe, ‘Kosovo 1999: The Air Campaign: have the Provisions of Additional Protocol I Withstood the Test?’ (2000) 837 International Review of the Red Cross 147.

[45] See, eg, C Greenwood, ‘New World Order or Old? The Invasion of Kuwait and The Rule of Law’ (1992) 55 Modern Law Review 153, 163–164; O Schachter, ‘United Nations Law in the Gulf Conflict’ (1991) 85 American Journal of International Law 452; and B Weston, ‘Security Council Resolution 678 and Persian Gulf Decision making: Precarious Legitimacy’ (1991) 85 American Journal of International Law 516.

[46] Cf E Rostow, ‘Until What? Enforcement Action or Collective Self-defence?’ (1991) 85 American Journal of International Law 506.

[47] The incidents involving direct civilian casualties appear to have resulted from faulty targeting or weapons failure.

[48] The loss of civilian life as a result of the coalition forces’ bombing campaign of Iraq has been widely criticised. See Report to the Secretary-General on Humanitarian Needs in Kuwait and Iraq, 20 March 1991, UN Doc S/22366 (1991), Report on the Gulf War, Amnesty International (1991); Needless Deaths in the Gulf War, Human Rights Watch (1991).

[49] See A Rogers, ‘Zero-casualty Warfare’ (2000) 837 International Review of the Red Cross 165. For the results of this policy on civilians and civilian objects, see Report on the Human Rights Situation involving Kosovo, submitted by Mary Robinson, High Commissioner for Human Rights UNHCHR Geneva 30 April 1999 and Human Rights Watch Civilian Deaths in the NATO Air Campaign. February 2000.

[50] See W Fenrick, ‘Attacking the Enemy Civilian as a Punishable Offense’ (1997) 7 Duke Journal of Comparative and International Law (1997) 539, 548–9, highlighting the difficulty in determining the obligations on a commander to expose his/her forces to risk. See also Reisman, above n 43, 861.

[51] See Rogers, above n 49.

[52] It is estimated that in 1998, refugees throughout the world numbered some 11 million and that the number of internally displaced persons was approximately five million. One of the major causes of such mass movements of persons is armed conflict and internal disturbances. See UNHCR, Refugee and Others of Concern to UNHCR — 1998 Statistical Overview, <> . See also R Falk, ‘Kosovo, World Order, and the Future of International Law’ (1999) 93 American Journal of International Law 847 (referring to estimates of a flow of approximately one million refugees resulting from NATO’s action).

[53] See Third Report on State Responsibility, above n 2, and Fourth Report on State Responsibility, Int’l L Comm’n, 44th Sess, UN Doc A/CN.4/444/Add1 (1992) (report by Gaetano Arangio-Ruiz).

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