So much for cosmopolitan justice. What about cosmopolitan war? In CW, I argued that the right to wage and fight in war is a right to kill and maim, or to authorize such acts, in defence of one’s and third-parties’ individual and jointly held human rights. I did not make it sufficiently clear in that book that the right can be held either by individuals taken singly (for example, by combatants who shoot at the enemy in defence of their life) or by individuals who each participate in a collective venture (for example, by each member of a platoon which embarks on a coordinated mission.) This is not to say, however, that the right to wage and fight in war should be regarded as irreducibly collective. Rather, it is to say that its participants’ acts of killing and maiming must be seen, not just or not only as individual acts of self- or other-defence, but also (at least often) as contributions to that enterprise. On that account, the fact that war is a collective enterprise remains firmly in view, but the right to wage and fight in war is still rooted in individualistic morality, since it protects values and interests which are constitutive of individuals’ flourishing and is held, not by groups whose moral status is irreducible to that of their members but by those individuals themselves.
This calls for a further remark. I include in participating agents those who, in fact, do not (e.g.) fire a single shot, or deliberately misfire. Although they do not directly cause enemy deaths, their participation in the war makes the latter, and its concomitant deaths, possible. It is in that sense that they can be deemed to contribute to the war, and it is why they are liable to defensive harm. The further question is whether they are liable to be killed for making that kind of contribution. I am inclined to think not, but also to say that they are liable to deliberate non-lethal harm, or to being exposed to a risk of a foreseen though unintentional lethal harm. In other words, they are to be treated in the same way as non-combatants whose contributions to an unjust war or phases thereof warrant harming, not killing, them.
Thus, the justification for the right to kill in war rests on causal contribution to an unjust war. If so, anyone who significantly contributes to an unjust war is liable to be killed—not just combatants, but non-combatants as well who significantly participate in the war effort, for example by working in munitions factories, or by taking the community to war in their capacity as its (civilian) leaders, or by directly funding pro-war media. Contrastingly, non-combatants who make a significant contribution to a just war are not liable to be killed. Admittedly, the notion of causal contribution, and the thought that causal contributions vary such as to issue in liability to different degrees of harm, are very problematic. Significance, counterfactual dependence, magnitude, and causal distance will in some cases give us an intuitively plausible account of ‘vary’, but in some cases not. The alternative is to abandon the view that causal contribution is decisive for establishing liability. But this seems too costly—for we do need a way to distinguish the bystander from the threat, and it is hard to see what else other than contribution (to a harm) can do the work. It seems, thus, that we have no choice but to endorse a plurality of interpretations of ‘causal contributions’. It is unsatisfactorily ad hoc, but there really is no other way, as far as I can tell.
So much, then, for the individualist framework of this book. Admittedly, I shall use throughout phrases such as ‘A wages an unjust war against B’, ‘A does not have the resources to do x , etc. Those phrasings should not be taken to suggest that I am, in fact and willy-nilly, conceiving of war and its constitutive rights and obligations in collectivist terms. By ‘A’, in such phrases, I do not mean ‘community A as a collective whose status is not reducible to that of its members and who, has such, wages an unjust war.’ Rather, I mean ‘those members of A who contribute in such and such ways to the war.’ (Incidentally, on this note, I shall refer to those members as citizens. In some cases, it would be more precise to say ‘residents’ or ‘taxpayers within A’. But given that the overwhelming majority of residents and taxpayers are in fact also citizens, I use the latter word for the sake of terminological simplicity.)
With those points in hand, we are in a better position to see whether the ethics of self- and other-defence in contexts other than war differs from the ethics of self- and other-defence in war. It is my contention (though I shall not defend it here) that the imposition of defensive harm is governed by the same norms in both contexts. However, one’s conception of those norms should appropriately reflect the specific features of those different contexts. Thus, what counts as a just cause for defensive harm, whether a particular kind of defensive harm is necessary, or indeed proportionate, is likely to vary across those contexts—not least because war involves high numbers of agents and thus high numbers of both simultaneous and diachronic threats.
Let me elaborate by reference to the act of killing—though what I say here applies to harm imposition in general. Much if not most of recent just war theory revolves around this very question—whether war violence is sui generis normatively speaking. Extant debates tend to conflate two questions: (a) is war violence sui generis? (b) is combatants’ right to kill in war justified in the same way as an individuals right to kill outside war? If one answers ‘yes’ to the second question, one is thereby committed to answering ‘no’ to the former. However, one may consistently answer ‘yes’ to the first, and ‘no’ to the second. For, in the latter case, one may hold that combatants, qua combatants, take part in a collective enterprise (war), and that justifying their individual acts of killing requires that one should take into account the fact that they act jointly with other combatants. At the same time, one may hold that the norms governing combatants’ acts of killing are different from the norms governing acts of killing carried out by collective agents outside war, such as the Mafia. Conversely, one may also consistently hold that acts of killing in war are justified on the same grounds and constrained by the same conditions as acts of killing outside war (thus, ‘no’ to the first question), and that when justifying such acts (and thus specifying those norms) one must consider whether the agent acted on his own when faced with a lone threat, as part of a group, etc. The latter position is the one I adopt throughout the book. It is an instance of what is now standardly called the reductive strategy for thinking about war. The reductive strategy construes the right to kill in war as a right held by individuals and not collectives; but it does not reduce all acts of killing in war to acts carried about by individuals each facing a lone threat and each acting on their own. 
In both contexts, however, an agent’s group membership (into a family, a tribe, a nation) is irrelevant to his or her designation as a legitimate target of defensive harm. This is of a piece with the central tenets of cosmopolitan justice: just as group membership per se does not affect the conferring of human rights and duties at the bar of justice, it does not affect the loss of those rights either. More precisely, in the context of war, combatants lose their right not to be harmed, not in virtue of their membership in a community which happens to be at war, but in virtue of unjustifiably subjecting third parties to a wrongful threat of harm. On that view, the moral status of the war ad bellum as just or unjust, together with the significance and relevance of individuals’ contributions to the war, does have a bearing on whether they have the right to kill enemy combatants or, conversely, whether they have lost their right not to be killed by them. Combatants who participate and fight in an unjust war act wrongly and lose their right not to be killed—or, as I shall sometimes say, are liable to be killed—whereas combatants who participate and fight in a just war do retain that right. In other words, and pace the so-called orthodox account of war as deployed by, e.g., Michael Walzer, the acts of killing committed by combatants in prosecution of an unjust war areprima facie wrongful whilst those committed by combatants in prosecution of a just war are prima facie justified.11 Finally, combatants have the right to kill enemy combatants only if the latter unjustifiably pose or contribute to posing a wrongful threat of grievous harm to third parties (otherwise put, unjustifiably use lethal force in violation of third parties’ human rights.) To say that they have the right so to act implies that the targets of their defensive force have lost their right not to be killed and are under a duty not to resist them. As we saw above, however, enemy combatants sometimes do not meet the requisite degree of contributory responsibility for rights violations and thus have not lost their right not to be killed, but it is nevertheless permissible either deliberately to inflict on them harm lesser than death, or foreseeably though unintentionally to kill them in prosecution of one’s just war. By the same token, it is sometimes permissible foreseeably and unintentionally to kill enemy innocent non-combatants—though not (crucially) on the mere grounds that they belong to the enemy but, rather, in justified defence of one’s personal prerogative to confer greater weight on one’s communal projects. If there is a justification for harming individuals who have not lost their right not to be harmed, one can say, not that their right has been violated (for there is a justification for so acting) but, rather, that it has been justifiably infringed.
As stated so far, my account of the right and permission to kill in war is neutral as between three different accounts of right and wrong to which Derek Parfit draws our attention. On the fact-relative account, an agent B is permitted to do x—in this instance, to kill another A—just if, were we to know all the relevant facts, killing A would be permissible. on the belief-relative account, B is permitted to kill A just if killing A would be permitted if her relevant beliefs were true. on the evidence-relative account, B is permitted to kill A just if killing A would be permitted in the light of the evidence available to B.12 Likewise, mutatis mutandis, with the claim that B has the right to kill A; and likewise, invertatis invertandis, with the claim that B commits a wrongdoing by killing A. Sometimes, those accounts yield the same conclusion; often, they diverge. Suppose that A unjustifiably poses a wrongful lethal threat to B. on a fact-relative account, B may kill A even if she neither believes nor has evidence that A is threatening her. But on both the belief- and the evidence-relative accounts, B may not kill A. Suppose now, by contrast and against the facts, that B mistakenly believes, or has false evidence, that A is trying to kill her. on the fact-relative account, B may not kill A; on the belief-relative and evidence-relative accounts, she may. As Parfit notes, which account we should endorse depends on whether we are asking what is the criterion for a right or wrong act, whether we are asking whether the agent is blameworthy for so acting, or whether we are asking what the agent may or ought to do if she does not know the relevant facts. Tackling those issues in full is obviously beyond the scope of this book, let alone this chapter. I shall simply posit the following theses. First, whether an agent is permitted or has the right to harm another solely depends on the facts of the matter, irrespective of both the agent’s beliefs and the evidence at her disposal. Second, whether an agent is blameworthy for so acting, when so acting is in fact wrong, depends not on her beliefs alone but on the extent to which her beliefs are informed by the best available evidence. Third, absent knowledge of the relevant facts, an agent ought to do that which would be permissible if the best available evidence fitted the facts. If the best available evidence does not fit the facts, the agent could be deemed to have acted objectively (or fact-relatively) wrongly though she would have been subjectively justified in so acting. In this case, if her objective wrongdoing consists in violating some other party’s right, she is liable to defensive harm; but to the extent that she is not blameworthy for so acting, she would also be excused (though not justified) for retaliating in her own defence. Unless otherwise stated, when I speak of agents’ post bellum right and duties, or of the rightness or wrongness of post bellum acts, I employ a fact-relative account thereof. 
So much, then, for the normative basis for the right and permission to kill in war. Central to the claim that, in a given case, an agent does have that right or permission, is the view that the end which he thereby serves is just. Whether this is so often depends on the degree to which that end is part of a just war. By a just war, I mean the following: (a) it has a just cause, where a just cause consists in the violation, backed by the threat of lethal force, of some party’s human rights; (b) it is a proportionate response to the injustice which the belligerent has suffered; (c) it is not fought and won through the deliberate and indiscriminate targeting of innocent non-combatants; (d) it stands a reasonable chance of succeeding by military means which do not breach the requirements of proportionality and discrimination; and (e) it is the only way to pursue the just cause.
Those principles call for six clarificatory points. First, I use the word ‘war’ to denote a violent conflict for political ends, where the number of victims is at least 1000 per year over the duration of the conflict, where casualties occur over several months, and where both parties are genuinely in a position to inflict harm on each other. This definition (which I adopt drawing on empirical studies of civil wars, notably the Correlates of War Project ) covers large-scale interstate wars, decades-long civil conflicts, as well as attritional struggles between insurgency groups. Many will undoubtedly object that interstate wars are a different kind of conflict altogether, subject as they are to the international laws of war and opposing as they do well-defined and easily identifiable belligerents and combatants. As I noted above however, on my account, wars are subject to the same norms as (collective and individual) interpersonal violence—hence my definition. Terminology-wise, the word ‘belligerent’ will refer to any community (whether politically sovereign or not) which is at war, while the word ‘combatant’ will refer to any individual who fights on behalf or at the behest of a belligerent. Throughout the book I shall generally refer to soldiers as combatants, largely because the word ‘soldier’ usually denotes someone who wears the uniform of a regular state army, to the exclusion of irregular fighters. The word ‘combatant’ encompasses both and, as my arguments apply to both, works better for my purposes.
Second, although the set of principles which are thought to govern war are standardly classified under the labels jus ad bellum, in bello, jus ex bello, and jus post bellum, those labels themselves are simply a convenient way of demarcating different phases in a ward4 They do not each constitute a set of substantially different and mutually independent normative principles. This of course is not how the tradition has tended to conceives of those categories. Thus, at various points in the history of the just war tradition, it has been held that the moral status of combatants’ acts of killing in bello in no way depends on the moral status of their leaders’ decision to resort to war ad bellum, which implies that those acts and decisions are governed by different moral norms. As we have just seen, however, this is not the case. Likewise, the principles of proportionality and necessity rule over both the decision to go to war and operational decisions once the war has started. And as we shall see throughout the book, requirements of proportionality, discrimination, and success apply with suitable modifications to the ending of war and to its aftermath.
Third, the just cause requirement, once unpacked, sets out justifications for resorting to war, whereas the other requirements delineate the conditions under which it may be waged and fought. Other things equal, a war which is unjust for lacking a just cause is more grievously unjust than a war which has a just cause but fails to meet other ad bellum requirements, for the latter at least has some justification (to wit, violations of human rights backed by the threat of lethal force) even if it does not fulfil constraining conditions on its resort. Thus, it is more unjust for A to go to war against B as a means to seize natural resources over which it has a claim though not one sufficiently strong to provide it with a just cause for war, even though there are alternative diplomatic routes to solve its conflict with B, than it is for it to go to war, in breach of necessity, when it has a sufficiently strong claim over those natural resources. 15
Fourth, by stipulating that the war should stand a reasonable chance of success, I do not mean to suggest that a war which only stands a minimal chance is ipso facto unjust. Suppose that there is a way of winning the war which would be proportionate, in the sense that the goods achieved are worth the harms caused in their pursuit; however, there is no certainty that the war will be won in that way; and if it does not succeed, those harms will be caused in vain. The question, then, is whether the mere fact that there is some chance of winning renders the war justified. The kind of goods which the war would bring about if successful makes a difference to how much of a chance of success the war should stand: a rather low threshold might be enough if the war seeks to avert a genocide, but not quite so if the war seeks to replace a foreign dictator with a properly authorized and indigenous regime.
Fifth, the requirement of proportionality needs closer attention in this context. In his seminal work on killing in war, Jeff McMahan distinguishes between wide and narrow dis/proportionality.  Take a domestic example. Suppose that unless I kill you, you will tread on my toes for five minutes, causing me considerable pain. If I do kill you, your relatives will launch a vendetta against my family. The claim that killing you is a disproportionate response might mean either that the harm I inflict on you is disproportionate in relation to the harm which you inflict on me, or that the bad consequences of my killing you are far worse (your death and that of several of my relatives) than the good it brings about (no treading on my toes). on the former count, my act is narrowly disproportionate; on the latter count, it is widely disproportionate. In the context of war, acts of killing are narrowly disproportionate to the extent that the good they bring about (achieving the just cause) is outweighed by the bad they occasion for those agents who are responsible for providing us with a just cause; they are widely disproportionate to the extent that the good they bring about is outweighed by the bad they occasion for, typically, non-participants. To illustrate: killing combatants who (e.g.) are not even firing at us a minute before the armistice comes into effect is narrowly disproportionate; holding position for a week only to retreat, at the cost of destroying a whole city’s water and electricity infrastructure, is widely disproportionate.
Sixth, it is sometimes said that war must aim to bring about peace, or (which is slightly different) cannot be just if its occurrence and/or the way it is fought undermine prospects for peace. In Rawls’ words, ‘the aim of a just war waged by a just well-ordered people is a just and lasting peace among peoples, and especially with the people’s present enemy.’  Peace, in this context, is not merely what peace studies scholars call negative peace, which is characterized by the mere absence of violence. Rather, it closely resembles what those scholars call positive peace, characterized by cooperation between erstwhile belligerents. More expansively put, peace as I understand it here is a state of affairs where all individuals actually enjoy their human rights to the freedoms and resources they need to lead a flourishing life. By implication, a just peace does not merely obtain between belligerents. It concerns all other parties who may have been wrongfully harmed by the war though were not themselves participants in it (e.g., bystander communities and their members whose infrastructure was damaged by mis-targeted bombs), as well as other parties who were neither harmed by the war nor contributed to it but whose prospects for a flourishing life partly depend on the peace settlement. For there to be a just peace, thus, it is not enough that belligerents no longer have a justified grievance against each other: it must also be the case that the rights of all human beings, wherever they are, are not violated in and by the aftermath of the war.18
Yet I have not added securing and not undermining prospects for peace as a sixth requirement for a just war. Securing such prospects folds into the just cause requirement, while not threatening them folds into the wide proportionality requirement. As they constitute a just cause for war, one may say of the victims of those violations that they are justified in resorting to war as a means to redress those violations—in other words, to secure peace. As for the claim that a war cannot be just if it fails to bring about a just peace, it is in fact a point about wide proportionality: on that view, a war is unjust if its occurrence and/or the way it is fought threatens the establishment of a just peace, precisely because the harms it thereby causes are widely disproportionate to the good it seeks to bring about. Suppose that As bellicose leaders mount an unwarranted invasion into B. B’s army repels the invasion successfully, but its leaders decide to overthrow A’s regime, on the grounds that only then will B be safe from future invasions at A’s hands. Although they are correct on this particular count, the fall of that regime leads to a murderously violent and long civil war within A. Although citizensB are safe, citizensA are not. In this case, B’s leadership may well have succeeded in securing peace between their compatriots and citizensA, but at a (widely) disproportionate cost.
In any event, the requirement that war not threaten prospects for a just peace is overly strict. For as we shall see throughout this book, it is not always possible or desirable for belligerents to seek a just peace: sometimes, all that they can and should hope for is a justified peace all things considered (henceforth, justifiedATC peace). A justifiedATC peace is a compromise between ensuring that individuals’ human rights are secure and acknowledging that realizing a just and peaceful world is simply not possible. I shall return to this distinction in s.1.5. Suffice it to say here that a state of peace between two erstwhile belligerents is not justifiedATC if the basic human rights of those belligerents’ individual members are compromised. Accordingly, although compromising on a just peace is sometimes morally justified, indeed sometimes morally mandatory, compromising on a j ustifiedATC peace is not morally mandatory, for one cannot expect of anyone to sacrifice their basic human rights—in other words, to allow themselves to be treated in de-humanizing ways.
So much, then, for war and its normative requirements. Our concern, though, is with peace after war. I describe my overall framework for the book in s.1.6. Beforehand, however, I offer a brief account of the just post bellum in the just war tradition.
-  I develop the point about non-combatants at some length in C. Fabre, ‘Guns, Food, and Liabilityto Attack’, Ethics 120 (2009): 36—63; see also J. McMahan, Killing in War (Oxford: Oxford UniversityPress, 2009), esp. ch. 5. For a recent attack on this kind of position, see S. Lazar, Sparing Civilians(Oxford: Oxford University Press, 2015). I am grateful to Victor Tadros for help in clarifying this(though he would, I think, reject my ‘plural interpretation’ move).
-  This paragraph expands on CW, 55. In this respect, my variant of reductivism differs from,perhaps, McMahans. See, especially, J. McMahan, ‘War as Self-Defense’, Ethics & International Affairs18 (2004): 75—80; and McMahan, Killing in War, 156.
-  See M. Walzer, Just and Unjust Wars—A Moral Argument with Historical Illustrations, 4th edn.(New York: Basic Books, 2006). I make that point in CW s.2.3.2. For classic statements of that view(modulo some differences which need not detain us here), see C. A. J. Coady, Morality and PoliticalViolence (Cambridge: Cambridge University Press, 2008); McMahan, Killing in War; D. Rodin, Warand Self-Defense (Oxford: Clarendon Press, 2002). For an excellent collection of essays on the debatebetween the orthodox and the neoclassical accounts, see D. Rodin and H. Shue (ed.), Just and UnjustWarriors (Oxford: Oxford University Press, 2008). The neoclassical account is rooted in the theory ofthe just war which was articulated in the Renaissance by Spanish scholastic thinkers, notably Franciscode Vitoria and Francisco Suarez. See F. Vitoria, ‘On the Law of War’, in A. Pagden and J. Lawrance(ed.), Political Writings (Cambridge: Cambridge University Press, 1991 ); F. Suarez, ‘De Bello’',in J. B. Scott (ed.), Selections from three works of Francisco Suarez, S.J: De Triplici Virtute Theologica,Fide, Spe, et Charitate (Oxford: Clarendon Press, 1944 ).
-  See D. Parfit, On What Matters, vol. 1 (Oxford: Oxford University Press, 2011), 150-62. For aclear application of the differences between those three accounts to liability to defensive harm, seeJ. Quong, ‘Liability to Defensive Harm’, Philosophy & Public Affairs 40 (2012): 45-77. See alsoMcMahan, Killing in War, 43; 173-5.
-  See http://www.correlatesofwar.org/ (accessed on 13/01/2016).
-  In fact, some people argue that on the reductivist strategy, those labels simply do not make sense,for the only objects of evaluation are acts of killing (or planning thereof.) See the debate on Peasoupon my paper ‘War Exit’, which forms the basis for ch. 2 of this book. (See http://peasoup.typepad.com/peasoup/2015/05/ethics-discussions-at-pea-soup-cecile-fabres-war-exit-with-critical-precis-by-helen-frowe.html accessed on 13/01/2016.) I still think that it makes some sense to speak of phases ofwar. Those phases do not always follow on from each other in a temporally linear fashion: a war mayoften stop and be followed by a fragile peace, only to break out again. This is particularly the case inasymmetrical conflicts marked by long, attritional periods of violence.
-  I defend the view that we ought to distinguish between a justification for a particular course ofaction and the conditions under which that course of action may be taken in Fabre, ‘Rights, Justiceand War’. For the view that wars to recover natural resources to which one has a claim are sometimesjustified, see CW, ch. 3. That view is heavily criticized in D. Rodin, ‘The Reciprocity Theory ofRights’, Law and Philosophy 33 (2014): 281—308; D. Statman, ‘Fabre’s Crusade for Justice: Why WeShould Not Join’, Law and Philosophy 33 (2014): 337—60.
-  McMahan, Killing in War, esp. 20—32.
-  J. Rawls, The Law of Peoples (Cambridge, Mass.: Harvard University Press, 1999), 94.
-  The founding father of peace studies, to whom the distinction between negative and positivepeace is owed, is Johan Galtung. See, e.g., J. Galtung, Essays in Peace Research (Copenhagen: Ejlers,1975). Some claim that the just peace requirement is dangerous, on the grounds that in striving tofulfil it belligerents are likely unnecessarily to prolong the war (see, e.g., Y. Beilin, ‘Just Peace: ADangerous Objective’, in P. Allan and A. Keller (ed.), What is a Just Peace? (Oxford: Oxford UniversityPress, 2008).