It was in 1953 that the Austrian poet Ingeborg Bachmann wrote, “War is no longer declared, only continued,” but she might well have written these words today. Eighteen years after the first U.S. airstrikes were launched against al-Qaeda (on October 7, 2001), the United States is still embroiled in Afghanistan. With some 14,000 U.S. troops still deployed there, this war has now surpassed the Vietnam War as the longest in the nation’s history. Just recently the eighth round of peace talks between United States and Taliban negotiators ended without a deal.

The concept of victory is now a question debated in a seminar room, not a fact easily recognized by a white flag on the battlefield.

In his speech to Congress three days after the World Trade Center attacks, George W. Bush defined the goal of his War on Terror. It “begins with al-Qaeda,” Bush said, “but it does not end there. It will not end until every terrorist group of global reach has been found, stopped, and defeated.” In this, he was right. Almost two decades later, not even al-Qaeda has surrendered, let alone “every terrorist group of global reach,” and the war goes on. By contrast, fewer than four years passed after the attack on Pearl Harbor before Japan and Germany unconditionally surrendered to the Allies.

Wars without definite ends are not unique to the United States, of course, nor are they all perpetrated against delocalized, non-state combatants. Syria and Somalia have been racked by civil wars for years, and decades-old conflicts continue to unfold in many places, from Kashmir to the West Bank. Shortly after he was appointed as Israel Defense Force’s new chief of general staff in January, Lt. General Aviv Kochavi announced plans for a three-day “Victory Seminar” for the military’s senior commanders. The goal was to clarify what, exactly, victory should mean in the next war the country fights. The very fact that such a discussion must be had at all is a telling indication of this new age of permanent conflict. Generals have traditionally been concerned with how to win a war, after all, not figuring out how to tell whether it has been won.  

The concept of victory, in other words, is now a question debated in a seminar room, not a fact easily recognized by a white flag on the battlefield. Wars may still begin like they always have, but they no longer end as they once did. As human rights and international humanitarian law scholar Gabriella Blum puts it, “contemporary conflicts blur the traditional lines between war and peace.” They “have no clear end-state.”

That lack of clarity has recently come in for renewed criticism in U.S. politics from across the ideological spectrum. Donald Trump has proposed withdrawing troops from both Syria and Afghanistan, though thus far he has failed to do so. Democratic presidential candidates Bernie Sanders and Elizabeth Warren have likewise called for ending the war in Afghanistan. While these appeals have reignited debate and helped to give U.S. foreign policy a more prominent place in news cycles, our public discussion of war still suffers from the lack of a clear and shared framework for thinking about how it should end. The difficult questions of Kochavi’s seminar remain peripheral and unsettled, namely: If we can’t clearly proclaim victory, and if we’re unwilling to accept defeat, when and how do we end a war?

This is a question not only for politicians and the military, but also for philosophers and ethicists. The absence of an ethics of conflict termination remains a major philosophical omission, one that hinders the civic polity’s ability to judge whether a conflict is or should be over. This omission vitiates a founding tenet of democracy: civilian control of the military. The lack of clear ideas about what constitutes legitimate goals in war and what constitutes victory or defeat makes it far too easy for military and political leaders to paint a misleading picture, and it makes it harder for voters to judge whether continuing a war is morally justified.

Moral considerations are often given short shrift in military or political assessments. At most, they are referred to as “humanitarian” considerations, one of the many considerations that decision-makers must take into the account. But this is a mistake, and one that deprives citizens of the moral language they need to demand justice in war. As new pressure is focused on ending the conflict in Afghanistan, citizens should be looking not only to politicians and generals, but also to philosophers and the new work being done in this space.


For millennia, philosophers and Christian theologians have worked on a framework for guiding the ethical prosecution of wars. Just war theory—the most influential source of objective guidance for the ethical prosecution of wars—is traditionally attributed to Ambrose (ca. 339-397 CE) and Augustine (354-430 CE). Nine hundred years later, Thomas Aquinas established the theological, systematic conscience-based foundations under which a war could be justified. Aquinas’s views became the model for later scholars, who universalized just war theory beyond its Christian foundations, recasting it in terms of what is allowed or forbidden in wars between modern nation-states.

The absence of an ethics of conflict termination hinders the civic polity’s ability to judge whether a conflict should be over. This omission vitiates a founding tenet of democracy: civilian control of the military.

Contemporary just war theory has branched into two schools—traditionalist and revisionist. The traditionalist camp is best represented by Michael Walzer’s seminal 1977 book Just and Unjust Wars, which defended a non-religious justification of national self-defense, combatant equality, and civilian immunity. In the last decade or so, a revisionist camp, spearheaded by Jeff McMahan’s work, questioned these tenets of traditional just war theory. McMahan’s book, Killing in War (2009), revolutionized the philosophical discussion on the ethics of war by questioning the moral standing of states and the justification of national self-defense as a just cause for war, problematizing the notion of civilian immunity, and systematically attacking Walzer’s argument regarding the moral equality of combatants—instead, McMahan contended that combatants fighting for an unjust cause have no right to kill.     

Historically, just war theorists distinguished between just two stages of conflict: jus ad bellum, the limitations on the resort to war, and jus in bello, the restrictions on the conduct in war. In the past twenty years philosophers in both camps—traditionalists and revisionists—have argued for adding jus post bellum as a third branch of just war theory as a way to provide guidance on what is owed after a conflict has ended. The construction of peace treaties and the reconstruction of states, for example, raise difficult questions about retribution and vengeance and what can be demanded of the defeated.  

Now, only more recently have philosophers started to address the gap between jus in bello and jus post bellum. As Cecile Fabre notes, “there is hardly any work on the transition from war to peace, and more specifically on the ethics of war termination.” As such, philosophers have begun arguing that the moral principles governing the end of armed conflicts require a new regime in just war theory, called either jus ex bello (Darrel Moellendorf’s terminology), or jus terminatio (David Rodin’s terminology). (The U.S. Military Academy at West Point is holding a conference on these subjects, called “How to End a War: Peace, Justice, and Repair,” just next week.) As Rodin puts it, such a framework should be a “fourth and independent component of the morality of war standing alongside jus ad bellum, jus in bello, and jus post bellum.”

Defining a framework for guiding the termination of wars, however, is not a straightforward task. You might start, for example, by just continually checking the conditions required to start a war. (Jus ad bellum requires meeting six distinct criteria.) Once the reasons that justified resorting to force do not apply any more, that framework would say, the war needs to be terminated. Yet this view simplifies the task at hand too much. First, the very fact that the war has begun has changed the moral situation. For example, there are those who already died in the war, new atrocities planned by the enemy could be discovered, or new, unpredictable costs, as well as termination costs, might emerge. Mechanical applications of the ad bellum principles could lead to morally perverse situations, since circumstances alter cases.

Second, and crucially, ad bellum conditions are not themselves the groundwork of the morality of war. They are the application of moral principles to specific situations, in which the two competing aims—to allow the victim to use defensive force while minimizing the harm of war—are balanced. To paraphrase Amartya Sen in his The Idea of Justice (2011), the task of a moral theory of ending wars is in “the prevention of manifest injustice in the world, rather than seeking the perfectly just.” To achieve progress in developing such a theory, we must recognize that there are differences in the moral evaluation between resorting to force and ending the use of force.    

But even if the ad bellum conditions are not the fundamental ones, they are nevertheless often of great practical importance. For this reason, it is useful to use them as a first approximation for whether a war is still just, or if it became unjust. Let me briefly explain, then, what the six ad bellum criteria are. First, a just cause typically means national self-defense against aggression. Right intention means, roughly, that a nation waging a just war should be doing so for a just cause and not for reasons of self-interest or aggrandizement, such as an excuse for territorial expansion. An act of war satisfies the principle of necessity only if there is no morally better way of achieving the just aim. A just war also needs to be initiated by a legitimate authority (generally, a government that represents its citizens and is internationally recognized). Proportionality means that the use of force must be proportionate to the achievement of the just cause. And achievability means that there must be a reasonable chance that the campaign for realizing those expected goals will succeed.  

The most crucial constraints on the continuation of using defensive force—and, thus, for war’s ending—are just cause, necessity, proportionality, and achievability. First, just cause: if a war has no just cause, it cannot be necessary and proportional. But without knowing the meaning of “self-defense” in contemporary conflicts (more on that below), it is impossible to consider whether it is necessary to use force in order to achieve it, whether the amount of force is proportional, and whether the cause is indeed achievable. Necessity, proportionality, and achievability are thus the consequentialist conditions of just war theory—the conditions which aim to tell us whether the use for force is still necessary, proportional, and achievable. Only by rigorous analysis of these conditions can we say whether a defensive war is still just.

So, how might these conditions be used in analyzing when a war should end?

First, note that in contemporary conflicts—where it is far more intricate to translate a military victory into a political one—these constraints are becoming increasingly difficult to assess. Few contemporary conflicts, after all, fit the nation-state model envisioned by traditional just war theory. Most contemporary conflicts are between a state and a non-state actor, or two non-state actors. In such conflicts, violence slowly ebbs and is replaced with unstable ceasefires. The fact that a defeated enemy may well persist as an influential political movement makes just cause and necessity especially difficult to nail down.  

As technology, military strategy, governance, and the nature of conflict change, so too must our legal and ethical theories regarding a war’s ending.

Consider globally active non-state organizations, such as al-Qaeda or the Taliban. Such organizations may be defeated locally, but their political apparatus could be far from the battlefield, protected from the fighting. A defense against aggression thus becomes impossible to secure because even a thorough military defeat may be of little political consequence as non-state actors seek mainly to alter public perception, not to win battles. They want to be politically empowered, which can happen both due to a military loss as well as a victory. Thus, the state’s usual calculation—military victory brings political victory—does not necessarily hold, and the condition of necessity is blurred. Just think of the many occasions over the years that U.S. generals have declared success on the battlefield in Afghanistan while insisting that any amount of troop withdrawal would still be disastrous for national security.  

The chief aim of ad bellum proportionality is to delineate reasons that tell in favor of resorting to force and those that tell against it. Political leaders must weigh the collective goods expected to result from resorting to force against the collective evils expected to result from it. Only then can we construct defensible conclusions about which options are necessary, proportionate, and achievable. To illustrate, consider Afghanistan again. If the United States’s 2019 goal is military victory over the Taliban, for example, then it is almost certainly not possible to achieve in a proportional manner, mainly due to moral costs. This fact was clearly echoed by Trump when he claimed last month that the United States “could win that war so fast if I wanted to kill ten million people there . . . which I don’t.”   

Consider also Israel’s gradual withdrawal from Gaza following 2014’s Operation Protective Edge. At the beginning of the campaign, it was relatively easy to damage Hamas at low cost to civilians because Israeli military intelligence had identified a “target bank”—important sites that could be hit without causing many civilian losses. But as the target bank was exhausted, remaining objectives were harder to achieve. Some were high-importance targets whose elimination entailed high costs—for example, the bunker housing Hamas’s top leadership was under a large hospital—while others were targets of little importance—say, a few Hamas fighters hiding in a civilian building.  

The desired military ends in both cases—the United States in Afghanistan and Israel in Gaza—are technically achievable, but they are also both grossly disproportional. In conflicts with non-state actors, as international law scholar Eyal Benvenisti observed, it is impossible to “compartmentalize the battlefield and single out with sufficient clarity military from civilian targets,” which makes it impossible to tell “whether the collateral civilian damage was or was not excessive relative to the effort made to achieve those goals.”

Proportionality, then, is deeply connected to achievability. Recall that achievability means, roughly, that there must be a reasonable chance that a military campaign for achieving the just cause will succeed. But as we saw, the old criterion of victory—overt surrender by a well-defined army or state—no longer applies. It has dissolved into the ambiguity of endless, shifting objectives, often against nameless, placeless enemies. As the philosopher and ethicist Moshe Halbertal has noted, “in ordinary war, the collapse of the enemy’s army is a more or less clear event; but in an asymmetrical war, victory is never final—the mission seems not so much to end as to shift.” Suppose that during the war it becomes clear that the original goal—say, eliminating al-Qaeda and the Taliban—is no longer achievable. Does that mean that the war must end? Or is it justifiable to allow the war to continue in order to achieve some part of the original just cause—say, toppling the Taliban—or even a different goal?

In the case of straight-forward conflicts, the achievability question sounds pretty simple: if military victory is unachievable, then surely the war must stop. But this view is mistaken. Instead of interpreting the achievability condition as an all-or-nothing criterion, I think it should be considered on a scale: What part of the original morally-worthy goal can be still achieved, and at what moral cost? Interpreted in this way, the achievability condition advances moral imperatives by framing the discussion of just cause and proportionality in relative terms. A robust achievability condition will advance moral imperatives by limiting the scope of legitimate goals political leaders may consider a priori—before any discussion of whether they are proportional.

This year, U.S. forces have been blamed for killing more civilian Afghans than the Taliban has—including a recent drone strike that killed more than thirty civilians.

The proportionality constraint also butts up against the problem of moral sunk costs. In the terms of just war theory, having incurred an amount of moral cost, it may seem unreasonable to require cessation if the original goal may be reached at a small cost beyond that which was initially deemed proportionate. As Abraham Lincoln put it in the Gettysburg Address, “From these honored dead we take increased devotion to that cause for which they here gave the last full measure of devotion.” Clearly, costs already expended could have major implications for the ethics of conflict termination.

The problem of sunk costs has proved among the most obstinate as the war in Afghanistan has dragged on. In 2015, for example, John McCain criticized Obama’s decision to gradually withdraw troops, saying: “All of us want the war in Afghanistan to be over, but after fourteen years of hard-fought gains, the decisions we make now will determine whether our progress will endure and our sacrifices will not have been in vain.”

While it is a point of contention whether it is morally justified to ever consider moral sunk costs in war, the crucial question we should ask ourselves is how can the fact that someone died in a war justify the death of even one additional soldier currently living? Even if sometimes it is justified for (a few) more to die so that (many) would not have died in vain, the next question we should ask is who should bear the cost, and whether there is a limit to the allowable number of future deaths. I cannot see why, for example, redeeming moral sunk costs should ever justify harming more innocent civilians—and in Afghanistan, the extra harm of continuing the war would be inflicted mostly on civilians. This year, U.S. forces have been blamed for killing more civilian Afghans than the Taliban has—including a recent drone strike that killed more than thirty civilians. This alone, I would argue, mean that moral sunk costs, in the case of Afghanistan and possibly in most contemporary conflicts, must not influence our decisions whether to continue the war.


The philosopher Jonathan Glover once wrote that “huge problems sometimes produce an irrational paralysis of the imagination.” Indeed, the decision on whether and how to end the war and withdraw U.S. troops from Afghanistan is much more complicated than, say, the decision to recall troops when Japan and Germany surrendered in World War II. But little in ethics is ever simple, and the difficult moral questions of when to end a war are no different. To more effectively confront the complexity we face today, the body politic must have a way to understand the moral perils of war and all of its options.  

In contemporary conflicts—where it is far more intricate to translate a military victory into a political one—the constraints of jus ad bellum are becoming increasingly difficult to assess.

There are reasons for optimism, I think. Consider, for instance, that in contemporary liberal democracies, it is widely accepted that the only justified wars are those of self-defense against armed aggression, and, perhaps, of humanitarian intervention. While common sense now, this attitude is by no means old: it is the result of the development of traditional just war theory over the last 150 years and the international legal regimes it has inspired. Before this time, war was usually seen as the sovereign’s prerogative—a “continuation of political activity by other means,” in the Prussian general Carl von Clausewitz’s dictum—and there was little concern for the enemy’s civilians or the enemy’s troops. Only by combined evolution of the moral (modern just war theory), the legal (the law on the use of force and international humanitarian law), and the socio-political (what wars the public would accept) did the public’s view of the morality of war change. The underlying motivation was changing circumstances and the evolving perceptions of societal values.

The same stands to happen today. As technology, military strategy, governance, and the nature of conflict change, so too must our legal and ethical theories regarding a war’s ending. An ideal society cannot be sustained without guidance toward prevention and termination of conflicts, which appear to be an inescapable dimension of human experience. Investigating the morality of war’s ending can, I believe, provide insight into the ideal peacetime society by illuminating legitimate goals and behaviors vis-à-vis other societies generally, not necessarily during armed conflict. To paraphrase Derek Parfit in his Reasons and Persons (1984), as our ethics catch up to our reality, it is not irrational to have high hopes.