Just and Unjust Wars

A Moral Argument with Historical Illustrations


By Michael Walzer

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“A classic in the field” (New York Times), this is a penetrating investigation into moral and ethical questions raised by war, drawing on examples from antiquity to the present.

Just and Unjust Wars has forever changed how we think about the ethics of conflict. In this modern classic, political philosopher Michael Walzer examines the moral issues that arise before, during, and after the wars we fight. Reaching from the Athenian attack on Melos, to the Mai Lai massacre, to the war in Afghanistan and beyond, Walzer mines historical and contemporary accounts and the testimony of participants, decision makers, and victims to explain when war is justified and what ethical limitations apply to those who wage it.


Preface to the Fifth Edition

The book of Ecclesiastes ends with a complaint: "Of making many books, there is no end." On the occasion of the fifth edition of Just and Unjust Wars, I can't complain about that; I am grateful for the re-making of this book. But it is also true that "Of making many wars, there is no end," and this should be a universal human complaint. I am writing just as the United States is ending two of the longest wars in its history (in Afghanistan and Iraq)—and beginning another (to degrade and defeat the Islamic State in Syria and, again, Iraq). Each new edition of Just and Unjust Wars has coincided with new wars and new questions about war. I wrote about humanitarian intervention in the preface to the third edition and about wars for regime change in the preface to the fourth.

As this latest edition is being prepared for publication, intense arguments are under way about asymmetric warfare—arguments that overlap a great deal with central issues in this book. But asymmetric warfare has its own set of moral difficulties and immoral cruelties that require specific, detailed consideration and judgment. For reasons I will come to, judgment is especially important—hence this newly prepared preface.

Most of the wars of the past several decades have been asymmetric; notably, for American citizens, the war against the Taliban in Afghanistan and the second Iraq war (after the first few weeks, when the success of the invasion produced an unexpected insurgency)—also the Israeli wars in Lebanon and Gaza, the Sri Lankan war against the Tamil rebels, and the Russian war in Chechnya. Asymmetric warfare isn't new; the guerrilla wars discussed in chapter 11, especially the Vietnam War, are earlier examples. Some writers believe that traditional just war theory, with its long-established rules about when to fight and how to fight, cannot deal with asymmetry. But if the theory "worked," as I think it did, in helping Americans understand what was wrong in Vietnam, there is no reason why it can't work in other times and places. It is a good theory; we remain indebted to the Catholic theologians who invented it centuries ago.

But the theory was invented to deal with what we now call "conventional" warfare—where two armies are engaged and each one is pretty much like the other in organization and armaments. If there are any rules that govern the fighting, it is easy to imagine that they will be the same for the two armies and for all their soldiers. Wars of that sort are—we should be thankful—rare these days. Iran and Iraq fought an old-fashioned war in the 1980s, and the 1991 Iraq war, against the conquest of Kuwait, was roughly conventional. We can all think of possible wars like those, but they are not likely to happen anytime soon.

In the more immediate conditions of asymmetry, by contrast, there is only one army, organized, armed, and disciplined by a modern state; its opponents are insurgents, less well-organized, less well-armed, and often without a coordinated system of military discipline or of military justice. Do the same rules apply to armies and insurgents? I want to say that they do, but that requires an argument.

The insurgents claim the prerogatives of weakness—which follow, they say, from the conventional doctrines of military necessity and last resort applied to their special circumstances. So the old rules do apply, but given the circumstances, not in the same way to the two sides. The insurgents have to be able to hide from the army's overwhelming firepower, so they can't wear uniforms. They can't fight along a "front"; they have to be able to strike anytime, anywhere, so they can't always distinguish combatants from civilians. In any case, military targets are often too dangerous for them to attack; killing civilians, they argue, is often the only thing they can do, so it is their "last resort" even if they don't actually try anything else. And they can't build fortresses or military bases, for if they don't have a "front," they also don't have a "rear" where they can assemble or regroup in safety. The only protection they have is the cover of their own people's homes and neighborhoods.

For the conventional army, insurgents claiming these prerogatives are a big problem. The army gets no circumstantial exemption from the old rules; it is expected above all to maintain the distinction between combatants and civilians, even if the insurgents deliberately blur the distinction. But how can its soldiers fight against enemies who hide among the civilian population without killing civilians?

The proportionality rule (see "The Argument of Henry Sidgwick" in chapter 8) is supposed to provide criteria for judging those deaths, but proportionality in warfare is not an exact science. Historically, in conventional wars, the rule has most often been read permissively: the value of the military target is so great that a fairly high number of civilian casualties (collateral damage, as it is called) is "not disproportionate." Think about an Allied decision to bomb a German tank factory in World War II. The factory is located in a working-class neighborhood—not for the sake of civilian cover but because that is where factories were built before workers had cars. Given the aiming devices available in 1943, any attack on the factory would kill many civilians. But the death of many civilians, indeed, of almost any number of civilians, is "not disproportionate" to the value of stopping the production of tanks for the German war effort. This same argument can be made, and was regularly made, in defense of attacks on considerably less valuable targets—which is the reason for my skepticism about the proportionality rule in this book.

In recent asymmetric conflicts, by contrast, the rule has been read restrictively. Asymmetry makes for micro-battles, small-scale engagements, and in these engagements, given the overwhelming power of the army and the weakness of the insurgents, even a very small number of civilian casualties seems disproportionate to the military value of the target. For the target may be nothing more than a couple of insurgents firing from the roof of a small apartment building (in Afghanistan) or a single rocket launching crew in the parking lot of a hospital (in Gaza).

The army argues that it has to respond to the gunfire from the roof and to the rockets from the parking lot, and the civilians it kills, even if their number looks disproportionate, are the moral responsibility of the insurgents who have chosen to fight from civilian cover. The insurgents blame the army's soldiers, who are indeed the actual killers; at the same time the insurgents commonly benefit from the civilian deaths in the court of public opinion. The weak are even more attractive when they are also victims, and it is probably true that insurgent fighters don't only hide behind civilians; they also deliberately expose civilians to attack. But the other side may also benefit from civilian deaths. The army aims, it says, only at military targets, but the collateral damage from its attacks may serve to deter future insurgent war making or discourage civilian support for the insurgents. So perhaps the army isn't as careful as it might be to avoid collateral damage.

Sorting all this out doesn't require us to abandon or significantly revise just war theory. It does require that the theory be applied, as the insurgents say, with close attention to the circumstances of asymmetry. Close attention is also critical attention: it doesn't necessarily support the insurgents' claims, nor does it allow just any military response from the army. But before addressing these battlefield issues, I need to consider, briefly, how the battles begin.

The army is, as it were, already in power, serving a sovereign state whose political policies and moral authority are contested, rightly or wrongly. So it's the insurgents who usually start the war. Claiming the prerogatives that I have just described, they often attack civilian targets, inviting a military response, the more savage the better. But how was the decision to attack reached? The insurgents are militarily weak, but they are not always or everywhere politically weak. They might have launched a political campaign against the policies and authority of the state—through repeated demonstrations, civil disobedience, a mass march, a general strike—and there probably were people in the insurgent organization who argued for this policy: politics before war. If war is the continuation of politics by other means, as Clausewitz said, then politics should come first; military force is supposed to be a "last resort," but even if that's not right, the use of force shouldn't come before or instead of political action (see my Arguing about War, chapters 6–7, for an argument about the metaphysical character of "lastness"). We should look for a political struggle in advance of any decision to go to war. It seems to me that the justice of the war, assuming for now the justice of the cause, hangs on this previous struggle. When war is not the continuation but the replacement of politics, we should probably call it unjust.

I am not going to say anything more about the causes for which insurgents fight; the recent history of asymmetric war includes a range of violent struggles—from national liberation to religious crusade. Most just war theorists would call the first of these just and the second unjust; that is my own view. But what is critically at issue in asymmetric warfare is less the cause than the conduct of the war. The focus on conduct derives from the extreme danger to which civilians are subjected, first by the insurgents and then by the army. How civilians are treated is a matter of jus in bello, justice in war, but it certainly reflects on the character of the insurgents and of the army (and of the state for which the army fights). A just cause can be undone if it is pursued in unjust ways. Or, better, when we condemn the conduct of an asymmetric war, we are also arguing that the cause, if it is just, must be pursued differently—by a different kind of war or by a return to politics.

Now, let's say, the fighting has begun, and the first attacks are aimed indiscriminately at civilians—with an argument attached: we can't do anything else. This is the standard argument in defense of terrorism, and it is hard to sustain, even if we set aside the political struggle that has just been pre-empted. Not every military target is impregnable to the insurgents. There are always vulnerable targets that can be attacked, if there is a will to attack them—as anyone knows who has toured the sprawling facilities of a modern army. Further evidence for this claim comes from inside the insurgent organization itself, where there are always dissidents who oppose attacks on civilians and argue for the possibility of a purely military campaign. They testify both to the strength of the conventional rules of war and to the weakness of the argument from necessity. I see no reason to give up on those rules; they apply also, as we will see, to the other side.

The insurgents can in fact distinguish soldiers and civilians among their enemies, and we should condemn every refusal or failure to do that. Their stronger argument is that they can't help their enemies make the same distinction—they can't separate themselves from their own civilians. Theirs, they say, is a popular insurgency; they fight from among the people because they are the people and the people are the insurgents. They aren't going to march off to some distant battlefield where they are certain to be overwhelmed. They will fight from where they live, or from where their people live, with whom they are one. Their human shields are volunteers, and if the insurgents benefit from the death of those shields, that is, from civilian deaths, they are not responsible for them. If the enemy army can't separate the insurgents from the people, it should give up, for there is no way that it can fight justly.

That is the primary argument of the insurgents, and it is much better than a common secondary argument: that they are fighting from such densely populated areas that they can't distance their fighters from residential neighborhoods. In the Gaza war of 2014, Israel claimed that some 15 percent of the rockets fired by Hamas were fired from residential neighborhoods and from schools, mosques, and hospitals within those neighborhoods. But if 85 percent of the rockets were fired from uninhabited areas, we have to conclude that the other firings were deliberately sited to provoke counterfire that would kill and injure civilians. Clearly the provocation worked. Population density is a problem for the army; I don't think it is an excuse for the insurgents. If the excuse isn't persuasive in Gaza, with one of the highest ratios of people to space in the world, then it must be far less persuasive in places like Vietnam, Afghanistan, and Iraq.

But the insurgents' claim that they are fighting from where they live, that they are at one with their people, is more plausible—though the claim obviously has different truth value in different countries, at different times. The closer the insurgents are to their people, the stronger the argument for oneness, the more likely it is that they won't be blamed for not wearing uniforms (think of the Minutemen in the American War of Independence) or for fighting from homes and neighborhoods. But when they fight that way, they cannot blame the army for the civilians it kills in response—so long as the soldiers live by the rules that still apply to them.

Many conventional wars have been fought in crowded urban neighborhoods; we shouldn't expect insurgents to miss the opportunities offered by cities and also by towns and villages. There is, however, a difference here: a conventional army, fighting its way through a city, will probably kill civilians, but these killings do not benefit the opposing army. In asymmetric warfare, the army's killings definitely benefit the insurgents, who are therefore liable to the charge, which I have already made, that they deliberately expose civilians to enemy fire. But suppose they have the support of many of the men and women they expose, from whose homes and neighborhoods they choose to fight. Then, indeed, the army responding to insurgent attacks will face a difficult and highly charged moral and political decision: how to deal with "the people," that is, with unarmed but possibly hostile civilians, who are indistinguishable from the insurgents.

Here is what I take to be the central issue in asymmetric warfare (it's also an issue in conventional wars, but asymmetry gives it special significance): How should the army fight when its fighting puts "enemy" civilians at risk? "Enemy" is in scare quotes because, while some of these civilians may well sympathize with or actively support the insurgents (as the insurgents claim), some of them do not; some of them just wish they were somewhere else. And there are always the children, one-third or more of the population, who aren't anyone's enemies. So the insurgents are fighting from among a mixed group of civilians; the army's soldiers are attacking. How should the soldiers plan, organize, and carry out their attack? The key moral issue can be specified more clearly: What risks should the army ask its soldiers to take in order to reduce the risks they impose on "enemy" civilians?

In a sense, the question is unfair. It isn't the soldiers' fault that they aren't fighting on a conventional battlefield against a uniformed enemy. The moral difficulties of asymmetric warfare are imposed on the soldiers, not chosen by them. Nonetheless, they are well-armed and well-trained, and they are backed up by all the resources of a high-tech military force; the civilians they encounter are unarmed and untrained, highly vulnerable, with no backup at all. And it is the soldiers who, whatever their own intentions, put those civilians at risk. I argue in this book, with examples from World War II, Korea, and Vietnam, that soldiers have to accept some risk (I don't attempt to say how much) in order to protect civilians from their own deadly fire. The revised version of the double effect doctrine that I describe in chapter 9, which sets up this question, has been widely discussed and adopted by many just war theorists. But the specific issue of risk taking didn't get much attention until the wars in Afghanistan and Gaza.

The moral burden I place on soldiers is unfair in another way. The insurgents don't take any risks to avoid putting civilians at risk; instead, they often take risks or, in the case of suicide bombers, they choose death precisely in order to kill and injure civilians. Soldiers are supposedly fighting to protect those civilians, so why make their fight harder and more dangerous? Why ask them to take risks to avoid killing "enemy" civilians whom their enemies are deliberately putting at risk? There is a pragmatic answer to this question: asymmetric war is also a political struggle—a battle for civilian support, that is, for "hearts and minds." The U.S. Army's revised rules of engagement for soldiers in Afghanistan, announced in 2010, were aimed above all at reducing civilian casualties. The rationale was very simple, and it fits many other asymmetric wars: you don't win hearts and minds by destroying bodies. But in Israel's Gaza wars, winning the hearts and minds of the inhabitants of the Gaza Strip was probably not a plausible war aim (though Israel certainly would have benefited if Gazans came to believe that the Israeli army was more committed to civilian well-being than the Hamas militants were). In any case, a similar pragmatic argument applies: it is global rather than local hearts and minds that are at issue now, but in international society as it is today the loss is equally damaging—or even more damaging.

Pragmatic arguments, however, only hold if they work—in this case if a significant reduction of collateral damage brings with it local support or global sympathy. The moral argument holds whether or not this happens: these people should not be killed, and these soldiers have an obligation to do everything they can to avoid killing them. It is possible, as some critics claim, that the effective meaning of this obligation is that the soldiers won't be able to win asymmetric wars. Asymmetry describes a struggle between a very strong and a very weak military force: a high-tech army against a low-tech insurgency. The difference in firepower is huge. And yet, throughout history, the army rarely defeats the insurgents; even when it doesn't lose the war, it doesn't actually win. The U.S. Army could not defeat the Vietcong in Vietnam; nor could the United States along with its NATO allies defeat the Taliban in Afghanistan; nor were we able to defeat either the Sunni or the Shiite militias in Iraq. The Israelis did not lose the wars in Lebanon and Gaza, but they can't be said to have won. It is indeed possible to win—by giving up on hearts and minds and on any semblance of moral decency and simply killing and killing until the insurgents' civilian cover is literally gone. The Russians in Chechnya and the government of Sri Lanka in its war against the Tamil rebels demonstrate that these wars can be won by a modern army. But can they be won by an army committed to just rules of engagement?

The answer to this question depends not only on the commitment and competence of the army but also on the moral/political judgments of everyone else, locally and globally. So it is important to condemn military actions that break the rules, even if these actions don't reach to massive attacks on the civilian population. The army must not look to benefit from the collateral damage it inflicts in the course of legitimate attacks on military targets; it must take positive measures to limit civilian injury. And these positive measures include soldiers accepting risk, to some degree, in order to minimize the risks they impose on civilians. One form of risk taking has been fairly common in both America's and Israel's wars: warning of attacks to come, so that civilians can flee—and insurgents can prepare, if that is possible, for the attack. It is a good thing to warn civilians of impending danger, but warnings are not sufficient. As American soldiers learned in Vietnam, many people don't leave: they are caring for elderly parents or sick children; they are afraid that their homes will be looted; they have no safe place to go.

There are, then, other things that must be done—and not done. Consider my earlier example of Taliban insurgents firing at American soldiers from the roof of a small apartment building in an Afghan town. The soldiers don't know who is in the building. They could simply pull back and call in an air strike—taking no risks themselves but radically endangering any civilians in the building. The 2010 rules of engagement rightly rule this out, so the soldiers have (in this simplified example) only three options: they can try to get someone into the building to see if civilians are living there, or they can try to get soldiers onto an adjacent roof, so that they can fire directly at the insurgents. Both these actions require the soldiers to accept (some degree of) risk. Or they can withdraw and wait for another encounter with the Taliban insurgents. No army likes to leave the battlefield to the enemy, but if the officer in the field thinks that the risks of the other options are too great, that is the right thing to do.

But what if there are civilians on the roof, dragged up there by force or willingly standing with the insurgents? And what if the army unit's withdrawal would leave other units, fighting nearby, at risk? Then, even if soldiers succeed in getting onto adjacent roofs, civilians will be killed or injured. Who is responsible for those deaths? If the numbers seem disproportionate to the military value of the building, as they probably will, given the restrictive understanding of proportionality, the army will be blamed. I believe, by contrast, that whenever soldiers have accepted risks in order to minimize the injuries they inflict on civilians, the blame should fall elsewhere. Calling in an air strike would probably be a war crime; killing civilians in a firefight in the circumstances I have just described is not.

Since attacks from the air, from planes or drones, involve no risk for the attacking forces, it might be argued that our judgments is these cases can only be shaped by calculations of proportionality. That may be true, and then we will need to find our way to calculations that are neither too permissive nor too restrictive. But successful air attacks, aimed at legitimate targets, depend heavily on information from the ground, and the collection of information is a dangerous business. Too often, attacks have been launched without sufficient knowledge about the targets or with knowledge provided by unreliable informants, who are often pursuing private vendettas. Many civilians die in attacks of that sort, which should always be condemned. But when the intelligence work is seriously undertaken and its risks accepted, and when civilians are killed because they are being used as cover or deliberately exposed, the army can rightly claim that it has done the best it could in the circumstances of asymmetry.

It is important to get these judgments right because, as I've already said, asymmetric wars are also political struggles. The insurgents, the soldiers, and the endangered civilians are not the only people involved; all the rest of us are involved. In a sense, this is true also in conventional wars. The point of writing a book like Just and Unjust Wars is to facilitate the judgments that citizens have to make about the wars their countries fight. But in asymmetric warfare, the responsibility to judge the war, to join the arguments about how it is being fought, extends more widely. The world's judgments are important, and if the "world" gets things right, the war will probably end with justice done.

The insurgents should be condemned when they attack civilians and when they deliberately put civilians at risk; they should be praised and supported when they struggle, in the circumstances of asymmetry, to fight justly. The army should be condemned when it fails to do everything it can do, in the circumstances of asymmetry, to avoid killing civilians, and it should be praised and supported when it lives by the moral rules of engagement. Strong judgments of this sort will promote good endings, and I suspect that in the long run the anticipation of strong judgments will make asymmetric wars less likely.


Michael Walzer

Princeton, New Jersey

May 2015

Preface to the First Edition

I did not begin by thinking about war in general, but about particular wars, above all about the American intervention in Vietnam. Nor did I begin as a philosopher, but as a political activist and a partisan. Certainly, political and moral philosophy ought to help us at those difficult times when we choose sides and make commitments. But it does so only indirectly. We are not usually philosophical in moments of crisis; most often, there is no time. War especially imposes an urgency that is probably incompatible with philosophy as a serious enterprise. The philosopher is like Wordsworth's poet who reflects in tranquility upon past experience (or other people's experience), thinking about political and moral choices already made. And yet these choices are made in philosophical terms, available because of previous reflection. It was, for example a matter of great importance to all of us in the American anti-war movement of the late 1960s and early 1970s that we found a moral doctrine ready at hand, a connected set of names and concepts that we all knew—and that everyone else knew. Our anger and indignation were shaped by the words available to express them, and the words were at the tips of our tongues even though we had never before explored their meanings and connections. When we talked about aggression and neutrality, the rights of prisoners of war and civilians, atrocities and war crimes, we were drawing upon the work of many generations of men and women, most of whom we had never heard of. We would be better off if we did not need a vocabulary like that, but given that we need it, we must be grateful that we have it. Without this vocabulary, we could not have thought about the Vietnam War as we did, let alone have communicated our thoughts to other people.

No doubt we used the available words freely and often carelessly. Sometimes this was due to the excitement of the moment and the pressures of partisanship, but it also had a more serious cause. We suffered from an education which taught us that these words had no proper descriptive use and no objective meaning. Moral discourse was excluded from the world of science, even of social science. It expressed feelings, not perceptions, and there was no reason for the expression of feelings to be precise. Or rather, any precision it achieved had an entirely subjective reference: it was the domain of the poet and the literary critic. I don't need to rehearse this point of view (I shall criticize it in detail later on), though it's less prevalent now than it once was. What is crucial is that we disputed it, knowingly or unknowingly, every time we criticized American conduct in Vietnam. For our criticisms had the form at least of reports on the real world, not merely on the state of our own tempers. They required evidence; they pressed us, however trained we were in the loose use of moral language, toward analysis and investigation. Even the most skeptical among us came to see that these criticisms could be true (or false).


  • "A magnificent book, an honor to its writer...a book that makes for a return of civilized discussion of the question of the morality of war."—New York Review of Books
  • "A passionate defense of the old principle of non-combatant immunity.... [Walzer] is both thorough and persuasive in his exploration of a very intricate subject."—Washington Post
  • "A classic in the field."—New York Times
  • "One of the most significant modern restatements of just-war thinking."—Nation
  • "A clear, humane, and startingly original survey of the moral issues that complicate modern war-making."—Atlantic

On Sale
Aug 11, 2015
Page Count
416 pages
Basic Books

Michael Walzer

About the Author

Michael Walzer is professor emeritus of social science at the Institute for Advanced Study, Princeton, NJ, and the author of many widely heralded books, including Spheres of Injustice, Exodus and Revolution, and The Company of Critics.

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