The just war tradition and its modern legacy: Jus ad bellum and jus in bello

Introduction

The idea of just war gives rise to three integrally related sets of issues. First, the justification of war itself as an instrument of policy or mode of conduct, often taken for granted by just war theorists and politicians alike. Hence the incongruent spectacle of Barack Obama receiving the Nobel Peace Prize on 10 December 2009, after outlining the criteria for a just war. Second, there are issues surrounding the conditions of the justifiable resort to war, which presuppose that war is a legitimate mode of conduct. These are questions of jus ad bellum, and invoke the deontological principles of just cause, the legitimate authority and right intention. All these criteria may be met, but it may still be imprudent or reckless to wage war. Hence, the consequences cannot be entirely ignored – giving rise to questions of last resort and proportionality. And third, there are issues relating to the conduct of war, questions of jus in bello, more commonly referred to as the laws of war or the laws of armed conflict. The justifications of extraordinary rendition and waterboarding are attempts to redefine the concept of torture and encompass such practices within the terms of reference of jus in bello. Post-1945 documents relating to jus in bello frequently refer to armed conflict instead of ‘war’ in recognition of the fact that the constraints apply irrespective of whether war has formally been declared, and to encompass armed conflicts within states. Both terms, the ‘laws of war’ and the ‘laws of armed conflict’, also include laws on genocide and crimes against humanity.

International conflict in Afghanistan and Iraq, precipitated by the events of 9/11, has generated a considerable wave of renewed interest in international humanitarian law, and in particular brought into sharp relief issues on the one hand surrounding the justness of causes of war, and on the other how these are related to the just conduct of the war (that is, the rules which regulate combatants, limit legitimate targets or objects during hostilities, and provide protection for the victims of war). The George W. Bush declaration of a ‘war on terror’ altered the terms of debate around jus in bello in that those perpetrating the ‘terror’ were no longer regarded as criminals but combatants. ¹ However, it was contended that they are not entitled to the protection of the laws of war under the Geneva Conventions because either they were fighting for non-sovereign actors such as Al-Qaeda, or fighting in non-sovereign territories such as in the failed state of Afghanistan. ² What was unusual was the de facto pronouncement legitimating resort to unlimited force, and the claim to be acting lawfully while suspending the laws of war. Indeed, the killing of Osama Bin Laden by American elite forces, the breach of Pakistani sovereignty, and the suspicious and contradictory accounts of the circumstances of his demise, indicate a suspension of the laws of war on which it is unlawful to kill an unarmed man.

Why does this constitute an issue or a problem? The fundamental or absolute presupposition of theorizing about war is the belief that civilization consists in the gradual elimination of force from our relations with others, and that recourse to force must require some sort of justification or explanation. If civilization is to be upheld, some way of regulating the conduct of armed conflict is imperative. This is what underpins Bluntschli’s famous dictum that ‘the law of war civilizes just and unjust wars alike’. ³ Implicit in the Bush attitude to the axis of evil is that combatants who do not fight under the auspices of a state, or are backed by rogue states, or even fight in territories in which sovereignty has broken down, are effectively outside of the ‘civilized’ world, and that the laws of war that apply within the society of civilized states do not apply to the same degree in relations between them and actors outside of that society. ⁴

Since the First World War the justifiable resort to armed conflict in relations among states has gradually been restricted and proscribed. Conceptually, it is possible to distinguish between the justness or rightness of a war and its legality. However, for many who wish to regulate the conduct of war, the moral question of the justness or injustice of a war is equivalent, or correlative, to claiming that it is legal. Those who authorize resort to armed conflict are required to justify its legality, and often do so by claiming just cause. The idea of the justness of war, however, has gained greater prominence following 9/11. The argument, particularly associated with George W. Bush and Tony Blair, that states have a right to anticipatory military action for self-defence is based upon the claim that such action is ‘just’. ⁵ The wars in Afghanistan and Iraq and the intervention in Libya have all been justified on the grounds of the justness of the cause (principally, in the Libyan case, the protection of human rights against gross governmental violation).

Whether one is convinced of the veracity of motives, there has not been – up until recently – any overt suggestion that the conduct of such military action is not required to satisfy jus in bello. Those associated with its just conduct need not, and in modern times do not, judge the merits of the claims to just cause (jus ad bellum). The international Committee of the Red Cross, for example, makes no judgements about whether a war is just, and on whose side right may reside. Furthermore, in most of the important documents constraining war the words ‘just’ and ‘unjust’ do not appear. This is the case for the Geneva Conventions, and the Hague Conventions and Regulations for Land Warfare. ⁶ It is acknowledged, then, by the international community that there will be occasions when threats to fundamental values, principles or interests are so great that resort to lethal force is justified in protecting or preserving them. ⁷ The moral justifications given for war usually imply limiting the contexts in which resort to force is permissible, and the manner of its use. As soldiers were reminded in the American Civil War: ‘Men who take up arms against one another in public war do not cease on this account to be moral beings, responsible to one another and to God’. ⁸ In other words, the contention that a cause is just does not permit unrestrained slaughter of the enemy.

Armed force is not forbidden by international law. States may lawfully resort to force with the authorization of the United Nations, for purposes of self-defence, and more contentiously perhaps for humanitarian reasons. ⁹ Security Council resolution 1973 (2011), for example, authorizes member states to take all necessary measures to protect civilians and civilian populated areas to prevent the serious violations of human rights and humanitarian law by the Libyan Arab Jamahiriya. The resolution implicitly endorses the justness of the ‘war’ between the rebels and Muammar Gaddafi’s forces by referring in article 2 to the ‘legitimate demands of the Libyan people’. ¹⁰ Both sides, however, in principle, are subject to humanitarian law, and each may justly be prevented from harming civilians. This example highlights how jus ad bellum and jus in bello overlap. As events unfolded, however, it became evident that it was a one way process which protected civilians against government forces, but not against the rebels. The Security Council resolution became a pretext for regime change.

If a state in the modern world has a right to go to war, it is a conditional right. But should the rightness or wrongness of a cause have any bearing on the manner in which war is conducted by the combatants, or indeed, on how one treats non-combatants? In this paper I want to explore the changing relationship between jus ad bellum and jus in bello and examine the reasons for the different positions adopted. There is no necessary connection between the two, and the relationship has been perceived very differently by the ‘authorities’ on the laws of war. Three of the towering figures in international political theory, Hugo Grotius, Samuel von Pufendorf and Emer de Vattel exemplify three important attitudes to the relationship between the justice of a war and its just conduct. To characterize them starkly, they are, first, that both the cause and the conduct of warfare must be just; second, that the cause must be just, whilst the conduct of the war is unconstrained; and, third, we must assume justice on both sides in the causes of war, and so ensure that the conduct of armed conflict is just.

All, of course, were to a large extent attempting to distil customary practices, which they often took as evidence for the precepts of Natural Law, while acknowledging that customary international law, or the voluntary Law of Nations, may modify, but not negate, Natural Law. Customary international law has, in the development of modern constraints on warfare, come to replace the idea of Natural Law, and to some extent has taken on its function as foundational to agreements and treaties in which constraints are specified. The classic jurists were at the forefront of determining what these constraints and practices were. International agreements have become a major source of humanitarian law, or the laws of war, but to limit oneself to the formal agreements in investigating the development of constraints on the causes and conduct of war runs the risk of distorting the form and substance of the law. Many of the constraints which currently operate are extensions by analogy of established customary practices. Custom has been a central pillar upon which many of the modern-day rules of war have been founded. Indeed, much of the discussion surrounding the laws by which those indicted were to be tried before the Nuremberg Tribunal, and the ad hoc Tribunals for the Former Yugoslavia and Rwanda, and the International Criminal Court sought to establish their authority by reference to the existence of state practice, opinio juris and the writings of such ‘authorities’. Returning to the classic international jurists gives us an insight into the genesis and development of the laws of armed conflict, and the by no means uncomplicated question of the relationship between jus ad bellum and jus in bello.

The Grotian perspective on the limitations on warfare

Much of the groundwork for Grotius’s position was prepared by classic jurists such as Gentili, who made a plea that the constraints on the conduct of war should be observed irrespective of whether the cause was just. He was not, of course, suggesting that wars may be waged even if there is no just cause, only that the just conduct of war is not dependent upon the justness of the cause. Indeed, for Gentili, justice is part of the definition of war. In the most succinct and precise definition to be found among the classic jurists, Gentili maintains: ‘War is a just and public contest of arms.’ ¹¹ Furthermore, just war requires ‘just and righteous arms’. ¹² In other words jus ad bellum and jus in bello were for him inseparable. Gentili contends that not only must there be just cause, but that in addition 'all the acts of the war must be just'. ¹³ Gentili suggests that war necessarily results in claims from both sides of the justness of their cause. The fact that one side has a more just cause does not mean that the other party has no justice on its side at all. If there is doubt about on which side justice lies, and both aim to achieve a just conclusion then neither side may be considered unjust. In fact it is very rare that justice self-evidently resides on one side in war, and it is much more often the case that each side has a just cause. The importance of this recognition is that Gentili is not merely looking at the constraints on the conduct of war from the point of view of the wronged party, but is emphasizing the applicability of the rule of law to both parties in the hostilities. ¹⁴

This position was developed by Grotius, and constitutes a significant element in the modern Grotian Tradition in international law. ¹⁵ Grotius wanted to subject the conduct of war to the rule of law and was therefore opposed to the principle of just necessity. A war is just if the cause and the conduct are legitimate. Grotius added to the criteria of a properly just war that it be conducted humanely. Warfare had become so endemic by 1625 that it threatened civilized life by undermining moral knowledge and destabilizing politics. Grotius provided a language and vocabulary which retrieved politics and integrated it with war and its conduct. ¹⁶ War did not begin where law ended, but was itself subject to the Law of Nature and of nations. ¹⁷ Grotius’s determination to formulate these constraints was precipitated by his observation that little restraint was exercised in entering into and conducting war even by Christian nations, a condition which ‘even barbarous nations ought to be ashamed of’. ¹⁸

Grotius believed that when the atrocity of crimes committed by other states was self-evident then wars waged to inflict punishment are legitimate. ¹⁹ Grotius employs the principle of equivalence, intrinsic to the retributivist theory of punishment, as a constraint on nations: ‘And indeed, by the Law of Nature those Things may be Acquired by just War, which are either equivalent to that, which tho’ due to us, we cannot otherwise get, or which damnifies the Injurer, but within the bounds of a just Punishment … .’ ²⁰

War and peace, generally conceptualized as opposites in contemporary thinking, were not for Grotius antithetical. The laws of war and peace are not separate categories. War could be a legitimate way of arriving juridically at peace. ²¹ All legitimate wars aim at peace and by implication have just causes. Drawing upon the Christian tradition from St Augustine onwards, Grotius identifies peace as the proper end of war, and a just cause with injury received or the prevention of injury. Right reason does not proscribe the use of force among nations; on the contrary, it prescribes it when rights are being violated in order to protect society. If authorized by a public authority wars may have the sanction of public opinion and right balanced in their favour, but are nonetheless illegitimate or unlawful if they do not have a just cause.

Grotius argues that even in the case of just wars moderation should be practised, claiming that his aim is to restrict the unrestrained licence of war to that which is permitted by nature, or to the choice of the better among the things permitted. ²² Restraint must be exercised in determining who and what constitute legitimate targets; the method and manner of attack; and the treatment of prisoners of war.

Apart from the moral implications, it is imprudent to destroy those things that may drive the enemy to despair. Grotius suggests that the enemy may be more difficult to defeat if he is driven to despair. To conduct warfare with moderation conveys the impression of confidence in achieving victory. Clemency may serve to conciliate the enemy and weaken his spirit. Grotius is not denying the right under the Law of Nations to kill or seize those loyal to the enemy. He is instead calling for compassion in the treatment of the enemy both on grounds of expediency and humanity. The obverse of this temperamenta Belli is that Grotius contends the Law of Nations permits the killing of all people in enemy territory. ²³ He maintains: 'when War is proclaimed against a Nation, it is at the same time proclaimed against all of that Nation… And that an Enemy by the Law of Nations, be assaulted every where.’ ²⁴ The exception is that slaughter of the enemy on neutral territory is prohibited in conformity with the rights of the prince who rules over it, and not because of any rights the enemy may have.

The Law of Nations may permit what the Law of Nature would condemn. Here either the Law of Nature has to be moderated by the Law of Nations, or the law of nations has to be altered to be brought in line with it. ²⁵ For example, the Law of Nations may prohibit things allowed by the Law of Nature. When the Law of Nature permits us to kill a person, it is indifferent to whether we do it by the sword or poison. The Law of Nations, however, at least among the civilized, prohibits the taking of enemy lives by poison. The custom was established for the general benefit and to mitigate the harm caused by the growing frequency of wars. ²⁶

Grotius argues that the rights of certain innocents must not be violated, including women who are not employed as soldiers, children, religious office holders, merchants and farmers, as well as prisoners of war. The killing of innocents cannot always be avoided. Grotius, following Aquinas, supports the idea of double effect, adding Vitoria's proviso of reasonable precaution, to condone the killing of innocents, as long as it is not intentional and instead a by-product of military action. It is a delicate matter of judgement because the harm caused by such unintentional killing of innocents must be outweighed by the good achieved. Grotius argues that even in circumstances where absolute justice does not condemn the taking of lives in war, it is often more conducive to goodness, moderation and a generous soul to forgive. The rules of virtue require sparing even one’s enemy’s life, except in extreme necessity to save one’s own, or in such cases where personal crimes deserve death. ²⁷ In essence, then, the safety of innocents is not sacrosanct, but strong and exceptional reasons amounting to just necessity are required to justify the violation of non-combatants. ²⁸

A just war, jus ad bellum, requires just conduct in the waging of the war, jus in bello. If the rules of war are disregarded the conduct of the war may be unjust and therefore unlawful. An unjust war may be mitigated by conformity to legally constrained conduct but the acts remain morally unjust. Those who fight in unjust wars, even in conformity with the laws of jus in bello, if they are to be considered for admittance into heaven, must repent. ²⁹

Pufendorf and the suspension of natural law

Pufendorf’s position shares with that of Grotius an insistence upon resort to war fulfilling the criteria of jus ad bellum (such as right intention and last resort). What distinguishes it, however, is the claim that, once war has begun, the injured party may resort to any means to bring about its conclusion, which is peace. Unjust modes of waging war, for many scholars, undermine the legitimacy of even a just war against an unjust belligerent. But whilst the criteria for judging jus in bello are different from jus ad bellum, they are not always clearly separated. In the theory of Vitoria, for example, the two sets of criteria are inadequately distinguished. The principle of just necessity determining the justice of going to war permits every course of action required to bring about a successful conclusion. ³⁰ In the context of jus in bello, however, Vitoria invokes moral criteria which impose constraints on just necessity. Vitoria is of the opinion that right intention determines the rightness or lawfulness of whether innocent civilians may be killed in war. Vitoria suggests that ‘it is never right to commit evil, even to avoid greater evils'. ³¹ If, as an unintended consequence of acts of war, innocent civilians are killed, it may be condoned on condition that ‘it advances a just war which cannot be won in any other way’, adding the proviso ‘that the evil effects of the war do not outweigh the possible benefits sought by waging it’. ³²

Pufendorf takes a much more unequivocal stance that has its foundations, in part, in a denial of the reality of international law. This does not mean that we are not regulated by the moral constraints of Natural Law. It is the morality rather than the legality of war that preoccupies Pufendorf. In so far as a belligerent puts itself outside of the Natural Law it is morally permissible to do whatever is necessary, even if it is extreme, to bring about peace.

Pufendorf was not unusual in giving short shrift to the question of the legitimacy of the use of war. ³³ A serious violation of the fundamental Laws of Nature places oneself outside of its protection. The obligation to observe the Law of Nature towards another ceases when that state or person does not observe that same law in relation to me. While war is against the natural condition of man nature does not sanction it, but if the Natural Law is violated against me I am placed in ‘a sort of subsidiary status’, namely war, ‘when our safety cannot be secured except by force’. ³⁴ Violations of the Natural Law were in the last resort rectifiable by resort to war.

War may only be embarked upon for purposes of securing peace, the natural condition of humanity. ³⁵ States have the same right as individuals in a state of nature to exercise their natural liberties in defence against ‘unjust violence’. ³⁶ Such threats contravene the first Law of Nature which forbids hurting people unjustly, and requires us to act humanely towards fellow human beings. War is not, however, natural. It is inconsistent with human nature and is permitted only in the absence of a ‘more appropriate means' of securing one's rights. ³⁷ The alternative may be arbitration by a third party which if favourable may add credibility to one’s cause. When it is apparent that an injustice has been done, recourse to means other than war should first be explored, such as a conference between the parties concerned; the use of arbitrators; or even the settlement of the dispute by lot. ³⁸ The use of arbitration also prevents one ‘from rushing into unjust and unnecessary wars because of greediness and lack of self-control’. ³⁹ In disregarding the Laws of Nature, a belligerent leaves little alternative in protecting one’s rights but resort to war. It is not to be viewed as an instrument of policy, however, but rather ‘a sort of extraordinary means of acting with one another' permitted by nature. ⁴⁰

Following from the issues relating to the use of force as an appropriate manner of resolving disputes, Pufendorf addresses those surrounding jus ad bellum. He was as anxious as Grotius that the justification of war include the principles of just cause and right intention. A defensive war, while regrettable, may be just if the desire to protect ourselves and our property against unwarranted aggression is the fundamental motivation. Offensive wars are particularly difficult to justify and the utmost caution should be exercised in establishing the facts of the matter, ‘as nature does not allow one to plunge into war on the slightest provocation, even when one is fully convinced of the justice of his cause’. ⁴¹ An offensive war may be just if it is waged to recover what is owed, and to secure reparations for injuries and damages sustained. It is justifiable to inflict harm in order to force the violator to undertake that there will be no repetition of the injury.

Success in war is not guaranteed by the justice of one’s cause. To embark upon war to resolve a dispute is tantamount to implicit consent to accept whatever outcome the vagaries of conflict may deliver. War is like a game of chance, with the risk of losing the wager. There can be no legitimate grounds for complaint if the outcome is adverse. ⁴²

A war is unjust, Pufendorf claims, if it is waged because of a desire to acquire ‘superfluous possession’, or to exercise power over another, or for the sake of gaining fame by oppressing others. Fear is not in itself sufficient grounds to attack one’s neighbour. ⁴³ While fear may precipitate the improvement of our defences, it cannot justify securing a guarantee of hostile intent by resorting to war.

Whereas Aquinas, Grotius and Bacon thought culturally abhorrent practices such as human sacrifice yield just cause for intervention and ‘punishment’ by violating the laws of nature, other writers are more restrictive. Vitoria, Suarez and Pufendorf restrict the range of causes that may be claimed as just. There is no justification for attacking other peoples simply because we disapprove of their practices and ceremonies. Where cannibalism is practised by heathens a Christian prince has no right to intervene. Only when innocent victims, such as those shipwrecked and forced to take refuge, are killed and eaten can a prince have a right of war against them, and only then when his subjects have been palpably harmed.

For Pufendorf the violation of the Law of Nature, as we saw, absolves those violated from observing the Laws of Nature in respect of the violator. Subject to the proviso that the end aimed for in war is peace, Pufendorf's view is that excesses in war are justifiable. In other words, there is no jus in bello. He forcefully maintains:

The Law of Nature obligeth Men to mutual Exercise of the Offices and Duties of Peace; and the Person that first violates them to my Prejudice, releases me, as far as lies in his Power, from paying any of those Offices to himself: And in Consequence, as long as he professes himself my Enemy, he gives me a Liberty to use Violence against him in infinitum. Especially since, if I am, not allow’d this Liberty, but necessarily obliged to confine my Violence within certain Bounds, and in no case to proceed to Extremeties; the proper end of War, whether Offensive or Defensive, can never be obtain’d. ⁴⁴

Without this licence to go to extremes, Pufendorf argues, an end to the war would never be in sight.

In Pufendorf's view, punishment requires a supreme sovereign, and is applicable therefore only within the state. The principle of retribution, that the punishment must fit the crime, is applicable only to civil tribunals where a superior authoritatively hands down the sentence, and the purpose of the punishment is primarily to reform the criminal. Essentially, then, proportionality does not apply in war. In this respect it is not unjust to return an injury that far outweighs the original injury inflicted by the enemy, because such acts are not to be likened to punishment in which the principle of proportionality comes into play. In other words, while upholding the principle of proportionality in the resort to war, that is in deciding whether the injury is sufficient to merit resorting to war, jus ad bellum, he denies it in the conduct of war, jus in bello. Here he is much closer to his predecessor Suarez and his successor William Paley, than to Grotius.

Suarez and Paley nevertheless cautiously qualify their arguments. Paley, for example, condones excessive conduct in war because it is consistent with a justifiable cause and the attainment of peace. He was, nevertheless uncomfortable with acts of barbarity, including ‘the slaughter of captives’, ‘the violation of women’ and the ‘profanation of temples’, ‘prohibited not only by the practice of civilised nations, but by the law of Nature itself, as having no proper tendency to accelerate the termination, or accomplish the object of the war’. ⁴⁵

The force used in war, Pufendorf argues, does not acquire its sanction from an authoritative superior in the international domain. The aim of force is not primarily to reform the offender, but to protect my security, property and rights: to secure such ends it is permissible to use whatever means I think will best prevail against such a person, who, by the injury done me, has made it impossible for me to do him an injury, however I may treat him, until we have come to a new agreement to refrain from injuries for the future. ⁴⁶

A sovereign is not obliged, then, to exercise constraint by conforming to commonly agreed customs among nations which temper the excesses of war. An unjust war, however, may partially be mitigated by conformity to such customs, allowing the violator at least to exhibit the saving grace of moderation in inflicting injuries. ⁴⁷

Pufendorf did nevertheless believe there are certain natural constraints which operate even in just wars. The Law of Nature of humanity restrains us from inflicting excessive violence, and moderates unnecessary vindictiveness following victory. Even if there were not a natural aversion to excessive violence, prudential considerations must come into play. In war, fortunes often reverse and the sensible ruler would be wise to moderate the licence which allows unlimited force in case one's actions are taken as exemplars by the enemy should the tables turn.

Vattel and the obligations of jus in bello

Emerich Vattel occupies a position which differs considerably from Pufendorf, but also deviates from Grotius. Grotius thinks that blame can be attributed to belligerents in war and their cause determined just or unjust. There may on occasion be some justice on both sides, but this is unlikely. Vattel, while requiring that wars must not be waged unless justice is on one’s side, nevertheless believes that it is almost impossible to determine on which side a just cause lies. Indeed, it is more likely than not that there is some justice on both sides, and that both may be considered to be waging a just war. The real issue for him therefore becomes the humane conduct of warfare.

Vattel contends that the nation has a duty to place its interests above those of other nations and, in order to promote its own happiness and advancement, to do whatever it can. However, he is far from advocating unrestrained violence or vindictiveness in order to achieve the ends of war. He explains that, 'I say every thing she [the nation] can, not only in a physical but in a moral sense, – that is, everything she can do lawfully, and consistently with justice and honour’. ⁴⁸ Even though Vattel considers prudence a virtue for sovereigns, he contends that it can never 'recommend the use of unlawful means for the attainment of a just and laudable end’. ⁴⁹ Not even the principle invariably proposed by realists, that the welfare of the people must be the supreme law of the state, permits immoral and unlawful acts to indulge in such conduct because they ‘would be pernicious to human society and productive of fatal consequences to all nations’. ⁵⁰ The common good of one's own people and the good of the great society of nations depends upon the rejection of means that are unjust and dishonourable.

Vattel, like Grotius, is ostensibly concerned to determine the just causes of war, but he goes on to introduce the practical considerations of being able to determine on which side justice resides. He makes a distinction between the grounds which justify war, and the motives which animate the state to enter into it. Even if the grounds for entering into war are just, the war may nevertheless be rendered unjust if the motives are suspect. Vengeance, hatred or the desire for conquest, all motives which lack virtue, constitute an abuse of the right to go to war and renders the cause unjust. The principal grounds for entering into war are self-defence and the maintenance of one’s rights. ⁵¹

The determination in practice of a just cause is, however, very difficult and we should proceed with a necessary element of caution. Both Vattel, and his mentor Christian Wolff, argue that – according to Natural Law – justice does not reside on both sides of a conflict. Each disputant assumes there are objective criteria by which to judge the justice of wars. Most states, nevertheless, claim in any particular conflict to have justice on their side, and each makes its own judgement concerning the injustice done to it. No authority stands above them to judge the rightness or wrongness of their claims. It is impossible for two contrary claims at the same time to be true, but it is possible for both parties to act in good faith. When the facts of a dispute are ambiguous, determining on which side right stands is increasingly more difficult. Wolff therefore concludes that according to the voluntary Law of Nations war must be considered justified for both parties. ⁵²

Vattel is convinced that both sides in a dispute may with equal sincerity claim to have right on their side, and when there is doubt both ‘the arms of the two parties at war are to be accounted equally lawful’. ⁵³ This does not deprive third parties of taking a view as to the justice of the cause on each side and acting accordingly. Attempts by neutrals to enforce the necessary Law of Nations during the conduct of war, however, are only likely to exacerbate the situation. A nation that acts in good faith out of ‘invincible ignorance or error’, according to Vattel, cannot be accused of injustice. ⁵⁴

It is unrealistic, Vattel contends, to think that both nations at war would not claim just cause in the context of a great society of equal sovereignty. Observance of the necessary Law of Nations is a matter of conscience from which no nation may be released. Reliance upon individual conscience, however, is not palpable enough. Something more certain in its application must be invoked. The voluntary Law of Nations fulfils this function.

Whereas the necessary Law of Nations, based as it is upon Natural Law, should always guide a sovereign's own conscience in formulating what he may demand of others, he should take account of the voluntary Law of Nations, which has accrued through custom and agreement, and whose precepts are designed to secure the safety and welfare of the great society of nations. In order effectively to constrain the violent methods to which states revert in war, we must presume for practical reasons with regard to its effects that justice resides on both sides. In essence, legal questions about the effects of war and the validity of claims of acquisition have to be separated from judgements about whether the cause is just. The voluntary Law of Nations does not pronounce on the justice of the cause. It therefore accuses no side, on the grounds of unjust cause, of using illegitimate methods. Because of the presumption of equal justification each side is permitted to do as the other. This is, in Vattel’s view, a practical expedient necessary for the regulation of war by law.

Vattel rejects the view that the voluntary Law of Nations makes what is wrong right. It does not confer true rights upon those who engage in war unjustly. In conscience, the acts are unjust, but through necessity and the determination to regulate the conduct of war the voluntary Law of Nations makes them legal and lifts the threat of punishment. ⁵⁵ For example, under the necessary Law of Nations a just title for acquisitions can only accrue to a combatant if his cause is just. Unjust action cannot confer a right to conquered property. In order to avoid endless disputes and fuel antagonisms the voluntary Law of Nations allows simple conquest as the basis of title without questioning the justice of the cause. ⁵⁶

Without using the terms, Vattel deploys one of the basic criteria in jus in bello, the distinction between combatants and non-combatants. In essence, he argues for non-combatant immunity. He acknowledges that all subjects of an opposing nation at war must be considered public enemies. Nevertheless, he insists that women, children, the aged and infirm, men of religion and men of letters, whose stations are distanced from military matters, have to be deemed non-resistant enemies. It would therefore be an injustice to assault them, let alone deprive them of their lives. ⁵⁷

The modern conception

The issues discussed concerning the three characterizations of the relation between jus ad bellum and jus in bello continue to surface in the modern period, and no one has gained permanent ascendancy. In 1914, for example, Wolff’s and Vattel’s position prevailed. It was considered beyond the scope of treatises on international law to draw a distinction between just and unjust causes of war. ⁵⁸ This stance was, of course, superseded by the horrors of the First World War and the attempts to regulate or outlaw a recurrence by the League of Nations and the United Nations. After the conclusion of the First World War we see a return to the Grotian position in which questions of the justice of a war begin once again to surface. The emphasis, nevertheless, has remained upon the laws of war, or jus in bello.

In relation to the modern laws of war which no longer had Natural Law as its foundation, the Law of Nations or the laws of war became more explicitly based on the codification of custom. An authority which stood outside of the disputants, and to which appeal could be made on questions of jus in bello, had to be found. Conscience, with the erosion of Natural Law, did not provide adequate enough constraint. Customary international law, which had always figured or been used to confirm or qualify the Natural Law, was invoked as a substitute to provide the function that Natural Law once did. No international body could claim the universal authority to ‘create’ fundamental humanitarian law, but such law as was found in customs could be codified and extended, and hence were foundational in relation to formal treatises and agreements. While the issues remain the same, although they appear in different guises, the foundation of the moral authority underpinning issues of jus in bello has changed. Custom itself lies at the heart of the moral obligation to act in a constrained manner.

Customs emerged from the earliest times in order to mitigate the ravages of war. For example, Thucydides in relation to the Greeks and Deuteronomy with reference to the Hebrews, testify to the customary prohibition on the destruction of vines and trees, which served the dual purpose of self-interest, as sources of food for future campaigns, and also the humanitarian preservation of non-combatants. Such customs, including the laws of chivalry, which served to mitigate the brutality of war, became widespread and deeply embedded in the practice of European warfare. They were so well established that both Edmund Burke and G. W. F. Hegel acknowledged them as part of the common law of Europe. Such practices as the preservation of the vines and trees of the enemy often became codified in international treaties and, where not directly applicable, extended by analogy. For example, article 55 of the annex to The Hague Convention, of 1907, No. IV, ‘Respecting the Laws and Customs of War on Land’ reiterates the duty to safeguard the forests and agricultural estates of the enemy. ⁵⁹

The prohibition on the use of poisoned weapons provides an example of how customary prohibitions are developed by extension and analogy. Both Grotius and Vattel contend that the customary law of civilized nations declares among the laws of war the prohibition of poisoned weapons. ⁶⁰ For Vattel their prohibition is justified by the Law of Nature, and on grounds of prudence: ‘if you poison your weapons, the enemy will follow your example; and thus, without gaining any advantage on your side for the decision of the contest, you have only added to the cruelty and calamities of war’. ⁶¹ The customary principles relating to the use in war of poisonous materials were codified and extended by formal conventions and declarations. Declaration 2 of The First Hague Peace Conference in 1899 derived its prohibition of the use of projectiles in war, designed to diffuse asphyxiating or deleterious gases, from the general principles of customary international law, and they also became embedded in the 1907 Hague Convention. Article 23(a) forbids the use of poisons and poisoned weapons. The prohibition was extended by analogy in the annex to The Geneva Gas Protocol of 1925 and the 1993 Chemical Weapon Convention. The Gas Protocol, for example, prohibits ‘the use in war of asphyxiating, poisonous or other gases, and of all analogous liquids, materials or devices’. ⁶² The 1998 Statute of the International Criminal Court which entered into force 1 July 2002 explicitly claims that it is codifying international customary law, and declares the employment of poison or poisoned weapons which cause death or serious damage to health by their toxic properties, as well as the use of prohibited gas, liquids and material devices, all war crimes. ⁶³

In addition, the exemption of fishing boats in pursuit of their vocation from seizure during war was a contested customary rule of international law, and an example of the development of the protection of non-combatants and their property, which was positively ruled upon in the The Paquete Habana case of 1900, following an incident in the American Spanish War, and codified in 1910 in a Note to Article 3 of The Hague Convention of 1907 which stated: ‘Vessels used exclusively for fishing along the coast… are exempt from capture’. ⁶⁴ The customary rules and conventions which came to regulate non-combatants, the wounded and surrendered, as well as the prohibition of weapons designed to inflict horrendous suffering disproportionate to the aim of weakening the enemy in war, became codified in the Geneva conventions of 1864, 1906, 1929 and 1949; the Declaration of St Petersburg of 1868; and The Hague Conventions of 1899 and 1907. ⁶⁵ Principles of jus in bello are, of course, closely tied to issues of human rights, but as Steiner and Alston suggest: ‘a war fought in compliance with standards and rules of the laws of war permits massive international killing or wounding and massive other destruction that, absent a war, would violate fundamental human rights norms’. ⁶⁶

The constraints on modern warfare recognized in the various conventions and declarations fall into two overlapping broad categories. The first covers the conduct of the conflict, that is, what methods are inappropriate; prohibitions on indiscriminate attack, especially against non-combatants; weapons which cause suffering far in excess of the aim of the war; and the outlawing of breaches of faith and treachery. The second group of principles are designed to protect non-combatants and those placed outside the conflict by means of illness; being wounded; shipwrecked; a prisoner of war; army medical personnel and the civilian population. These two bodies of law were updated and merged in the Protocols additional to the Geneva Conventions of 8 June, 1977. The Four Conventions and two Protocols constitute the principal body of regulations concerning the conduct of war. The whole body of treatises and customs together comprise what is called the ‘international humanitarian law of war’. Its purpose, as the St Peterburg’s Declaration of 1868 famously declared, is to alleviate ‘as far as possible the calamities of war’. ⁶⁷ These examples demonstrate the extent to which customary international law, which was once inextricably tied to Natural Law, continue to be of crucial importance now that their relation to Natural Law has ceased to be an issue.

These, then, are the laws of war, or of jus in bello, which currently prevail, but how, if at all, are they related to the rules of just cause, or jus ad bellum? If they are independent of each other, then the principles of the justice of the conduct of war are equally applicable irrespective of the justice of the cause. If adherence to the rules of jus in bello is somehow dependent on the justness of the cause, then two positions may be adopted. A war of aggression considered an unlawful act and constituting the ultimate international crime is beyond regulation and therefore the laws of war do not apply to either of the belligerents. This is a position that few would be inclined to support. It requires taking war outside of the rule of law, and suspending the rules of morality as far as armed conflict is concerned. Alternatively, an act of aggression, as we saw in the case of Pufendorf, suspends or deprives the aggressor state of the rights conferred by the rules of jus in bello. The victim of aggression, however, is free to violate those laws in whatever way it chooses.

The question arises, to what extent does the victim of an unjustifiable war, that is, the victim of aggression, have an obligation to alleviate the calamities of war, or to act proportionately in relation to weakening the enemy in war? Of the three positions outlined, and exemplified by Grotius, Pufendorf and Vattel, the Grotian tradition has prevailed, but not without equivocation.

The issue arose at the International Military Tribunal at Nuremberg. The UK Attorney-General argued strongly that the killing of combatants is legal in international and national law only when the war itself is legal. Wars perpetrated in violation of the Pact of Paris and without any sort of declaration are clearly illegal, and there is nothing to distinguish the killing from the murders of the victims of lawless robber bands. This view was, however, strongly rejected by the Tribunal. It maintained that a state acting justly in self-defence is not justified in disregarding the laws of war. In other words, the aggressor whose cause is unjust is nevertheless entitled to the protection of the laws of war and is equally obliged to conform to their constraints. ⁶⁸

The argument that the state which is the victim of aggression should be absolved of any obligation to comply with the laws of war continued to have its defenders. The Democratic Republic of Vietnam submitted a document in 1974 in support of the differentiated application of humanitarian law. ⁶⁹ The arguments in favour of such a position may include moral considerations, such as the contention that justice demands that we draw an absolute distinction between aggressors and victims, condemning unconditionally the former, and that therefore each should not be placed on an equal moral footing. Humanitarian law should aid the victim and hinder the aggressor. Similarly legal arguments may be made, such as the contention that the aggressor has committed the ultimate crime, and therefore placed itself outside of the law, absolving the victim of any obligation to comply with the rules of law. The fundamental legal principle that the criminal should not benefit from an unlawful act (ex iniura jus non oritur) may also be invoked. The practical result of such arguments is the separation of rights and duties, or obligations. The aggressor state has all of the duties and obligations and none of the rights with respect to jus in bello, while the victim has all the rights and none of the obligations.

In so far as elements of society in Afghanistan and Iraq consider themselves the victims of unlawful aggression, this is an argument that justifies guerrilla and unconventional warfare against the ‘enemy’ and its collaborators, yet protects the ‘victims’ from violations of the rules of war by the aggressor. It is arguable that de facto as a result of United Nations Resolution 1975 (2011), the rebels in Libya had all the rights and none of the obligations. The Libyan army had an obligation to desist from the injury of its own citizens, whereas the active destruction of Libyan forces by NATO assisted the rebels in attacking towns en route to Tripoli.

The argument that counters the abjuring of victim’s obligations, and aggressors’ rights, the position attributed to Pufendorf, derives from one of the opening remarks of this article. Civilization, and civilized conduct, or civility, presupposes the gradual elimination of force in our relations with fellow citizens, and between citizens of different bodies politic, at the heart of the arguments presented by Grotius and Vattel. ⁷⁰ Implicit in the argument placing right on one side (the victim’s) and obligation on the other (the aggressor’s) is that it requires placing belligerents outside of the moral realm, withdrawing the protection of the law, dehumanizing them in justification of the enormity of the brutality perpetrated upon them.

A number of considerations apply here. Is it possible to forfeit one’s rights in this way? The army of a belligerent state, whose cause is not just, is not responsible for the decision to go to war, and indeed, as long as the soldiers do not violate the laws of war, they may be absolved of blame. Customary international law, which is the foundation of the laws of war and armed conflict, has embedded in it the fundamental principle that the rights of opposing belligerents to inflict unlimited injury on the enemy is restricted and constrained. Humane considerations remain even in conflict irrespective of the justice of its cause. Here both the Grotian and Vattelian position agree.

The principle was incorporated in the 1874 Brussels Declaration, and the 1880 Oxford Manual. International law codifies it in the 1899 and 1907 Hague Conventions; the Geneva Conventions; the interpretation of the International Committee of the Red Cross, and the position taken by the Diplomatic Conference on the Reaffirmation and Development of International Humanitarian Law (Geneva 1974–7, particularly the Geneva Protocol, article 35(1)). All confirm the autonomy of jus in bello in relation to jus ad bellum. Adam Roberts and Richard Guelff justify the separate consideration of the laws of war by referring to the ‘cardinal principle that jus in bello applies in cases of armed conflict whether or not the inception of the conflict is lawful under jus ad bellum’. ⁷¹

This ‘cardinal principle’, however, has been tarnished by the claims of exceptionalism since 9/11 and the change of status of ‘terrorists’ from ‘criminals’ to combatants. The Bush declaration that combatants of non-state actors, of rogue states, and in territories where sovereignty has broken down, have no justifiable claim to the protection of the laws of war constitutes a change of direction in which wars of terror are by definition ‘unjust’, and legitimate at least the partial suspension of the laws of war.

As events unfold in Afghanistan, Iraq and Libya the relationship between jus ad bellum and jus in bello is considerably blurred, as it had been in Vietnam, by the unconventional character of the warfare. The concept of just war has been invoked in relation to all three recent conflicts. In Libya, for example, the just cause for intervention was explicitly to prevent the government forces killing innocent civilians. The way in which that mandate has been prosecuted and extended without an additional resolution of the UN, the issue of jus ad bellum, has led to the obfuscation of issues of just conduct and the application of the rules of armed conflict, jus in bello.

Above all, what all three conflicts bring into sharp relief is a third category of principles that are barely articulated throughout the history of reflection on jus ad bellum and jus in bello, but potentially catastrophic in their absence, and that is the principles of post bellum which relate to issues of just cause in the sense that resort to war must not only require a reasonable chance of success, but also the condition that the harm caused must not outweigh the benefits. There always were, of course, customary rules articulated by those who subscribed to the positions of Grotius, Pufendorf and Vattel regarding the conduct of occupying armies. Peace is not a clear enough objective, and this criticism may legitimately be levelled at traditional just war theorists, and modern perpetrators of armed conflict alike. In order to establish and maintain peace, post bellum requires a strategy for reconstruction, not just destruction. This requires clearly articulated objectives for jus post bellum. Such principles and objectives were not clearly articulated for Afghanistan, Iraq or Libya, beyond vague and vacuous appeals to democracy and justice. Exit strategies in all three conflict zones have implicitly abandoned the idea of jus post bellum and replaced it with ‘order’, whatever that may entail, to accelerate withdrawal of allied forces.

We may conclude that the relationship between jus ad bellum and jus in bello is in a state of flux. Formally, the Grotian position predominates. Since the First World War the emphasis has been on the justice of resorting to war and politically the unconditional subscription to principles of justice in conducting war. The Red Cross in upholding the impeccability of its neutrality in armed conflicts pursues the Vattellian position of assuming justice resides on both sides and concentrates only on jus in bello. Whereas both positions were related to Natural Law and derived their moral authority from it, modern iterations have replaced Natural Law and enhanced and developed the customary character of prohibitions and constraints. Custom itself was part of the classical jurists’ vocabulary, but was always qualified in some way by Natural Law. Customary international law now serves the function of Natural Law in that even if treatises in which it is articulated lapse the customary constraining precepts remain. Since 9/11, with the conversion of what were formally regarded as criminals into combatants in the war against terror, there has been a growing emphasis on jus ad bellum and a relative silence on the principles of jus in bello. Implicitly, but not formally, the balance is moving in the direction of Pufendorf’s position in which the ‘outlaw’ combatants, as a consequence of their actions, have placed themselves outside of the protection of customary law (Natural Law), and armed conflict against them is not subject to the same constraints. ⁷²