Planning for War’s Aftermath

Traditionally, just war theory has focused on two questions: what are the moral rules governing the initiation of war (jus ad bellum), and what are the moral rules governing conduct in war (jus in bello)? A third question has historically received much less attention: what does morality require after war (jus post bellum)?

This asymmetry is reflected not only in theory but in international law and institutions. There’s the UN Charter, which regulates the reasons for going to war. There are treaties such as the Hague and Geneva Conventions that regulate conduct in war. There are institutions like the International Court of Justice and the International Criminal Court that (attempt to) enforce these constraints. Nothing remotely comparable governs the postwar. There are no comprehensive treaties, institutions, or legal frameworks specifying what belligerents owe once hostilities end. What exists is fragmentary at best.

And so it is a welcome development that theorists have recently begun to take the subject of jus post bellum more seriously. But it’s a field in its infancy, and many foundational questions remain underexplored. One such question concerns the relationship between jus post bellum and jus ad bellum — in particular, whether the justification for going to war in the first place might depend in part on what one is able to do after the war.

The question is salient in the light of recent military operations in which decision-makers have shown little interest (at least publicly) in planning for the aftermath. By all appearances, considerations of postwar mitigation and compensation have carried no weight in Israel’s decision to go to war in Gaza in October 2023 or in the US-Israeli decision to go to war in Iran in February 2026. This apparent lack of postwar planning has been widely criticized on strategic grounds. My interest here, however, is not strategic but moral. Is it a requirement of morality that one have a postwar plan before going to war?

Is a postwar plan always required?

If it is, the traditional just war framework is incomplete. By neglecting jus post bellum for so long, the tradition would have failed to identify all of the relevant constraints on the initiation of war. The standard jus ad bellum principles are (roughly stated):

• Just cause: a state better have a good reason for going to war (e.g., self-defense against imminent aggression).

• Legitimate authority: wars should only be launched by legitimate states.

• Probability of success: don’t go to war if you don’t think the just cause has a good chance of being achieved.

• Last resort: only go to war if less-harmful means of achieving the just cause won’t do.

• Proportionality: the harmfulness of going to war can’t be too great compared to the importance of the just cause.

These are traditionally understood as conditions that must be satisfied for any war to be just. If a viable postwar plan were likewise always required, we would need to add an item to this list.

But it’s implausibly strong to claim that a postwar plan is always required. Formulating a viable postwar plan requires (among other things) resources, time, and information — prerequisites that are sometimes absent even when war is morally justified. Suppose, for example, a very poor country must defend itself against aggression from a neighboring country, and must do so in a way that damages the infrastructure and economy of the aggressor. The very poor country may know that they will be unable, after the war, to rebuild what they damage, which would make it impossible for them to establish a viable rebuilding plan. But surely that doesn’t imply that they are morally forbidden from starting a war of self-defense.

Likewise, suppose a nation is attacked by surprise, and must make an immediate decision whether to start a war of self-defense. Time would not permit planning for the postwar before initiating the war. But again, surely this doesn’t imply that the nation may not defend itself. Or finally, suppose a nation must decide whether to go to war under conditions where there are simply too many unknowns to make any sort of determinate postwar plans. The United States was arguably in such a position upon entering the Second World War. There were so many actors involved and so many theaters of combat that it may have been impossible, in 1941, to predict where reconstruction would be most needed and who would be available to participate in that reconstruction. Information was a scarce resource that would have made even a schematic version of the Marshall Plan impossible. That did not imply that the United States lacked a justification for entering the war. We should therefore reject the overly strong claim that postwar planning is always required.

Is a postwar plan never required?

But we should also reject the opposite extreme according to which postwar planning makes no difference at all to whether a war is justified. This view is also too strong, which we can see by considering a domestic analogy. Consider a case in which an aggressor attempts to kill Violet. You can defend her, but only by using a weapon that would poison the village well, causing a dozen neighbors to become gravely ill — so ill that they would die without medicine. And suppose that the medicine will be available only if you plan, in advance, to procure it.

In this case, whether or not you plan ahead to procure the medicine clearly makes a difference as to whether you should defend Violet. Indeed, it might make a decisive difference: it might be impermissible to defend Violet if you haven’t planned to procure the medicine, but permissible if you have.

The reason that planning for the medicine makes such a difference is because it makes a difference as to whether defending Violet is proportionate. When we talk about the use of force being proportionate in this sense, we are talking about whether the benefits of that use of force are great enough to justify the harm done. Killing five innocent people to save one innocent person would be plainly disproportionate — because the benefit is not great enough to justify the costs. On the other hand, saving one-thousand innocent lives would justify causing the death of one innocent person as a side-effect; that would be proportionate. (There are, of course, difficult questions about where to draw the line in between such clear cases of proportionate and disproportionate uses of force. But we needn’t settle that difficult question for the purposes of the matter at hand.) We might think of proportionality in terms of a balance: the benefits on one side and the costs on the other.

In the Violet case, whether you are able to procure the medicine makes a difference to proportionality because it makes a difference as to what is on the “cost” side of the balance. If you have access to the medicine, then you can prevent yourself from causing deaths-by-poisoning that you otherwise would have caused. You prevent those would-be costs from ever entering into the cost side of the balance in the first place.

Postwar planning and proportionality

We should think about postwar planning in the same way. Such planning, we’ve seen, isn’t strictly a necessary condition on the justification for going to war. But this doesn’t mean that it isn’t of great moral importance. It doesn’t introduce a new item to the classic set of jus ad bellum principles, but it nonetheless contributes to one of the principles already on the list: the proportionality principle.

Postwar planning bears on proportionality in two distinct ways: by preventing harms and by offsetting them. First, postwar planning will sometimes prevent our military conduct from resulting in more harm, after the war, than it otherwise would. Postwar planning is in this way preventative. To illustrate, suppose that we are considering a military operation that would cause economic damage to another country. This economic damage, we expect, will continue to cascade after the war, gradually making the citizens of that country poorer and poorer. If planning for postwar reconstruction would enable us to be more effective at forestalling this cascade more quickly, then such planning would prevent us from causing as much economic harm as we otherwise would. In this case, planning for the postwar, before the war, would prevent certain harms from ever entering the “cost” side of the proportionality balance, thereby making it easier for the war to satisfy the ad bellum proportionality constraint.

But preventing harm isn’t the only way of making it easier for a war to satisfy proportionality. In contrast to preventing certain costs from entering the “cost” side of the balance, we might also offset certain costs that have already entered. One way to do so is by compensating people for harms they have already suffered. Return to the example of Violet and the village well. Suppose that, although no one will be killed by my defense of Violet, there is no amount of planning I can do that will prevent my neighbors from suffering serious, non-lethal injury. Even though there is nothing I can do to prevent these injuries, it might still make a decisive difference whether my planning can ensure compensation for these injuries. If the injuries are serious enough, my ability to pay compensation might make the difference between my having a justification for defending Violet and my lacking one.

The same will be true in the case of war. Suppose we are considering a military operation that will displace thousands of people from their homes and render them refugees, and that there is no amount of planning that will prevent this outcome. Still, we might make it easier to satisfy the proportionality constraint on going to war by offsetting (rather than preventing) this harm, in the form of compensation. This compensation needn’t take the form of cash. It might instead take the form of reconstruction or asylum.

The upshot is this. Although postwar planning is not a universal precondition on the permissibility of war, it is nonetheless morally weighty (and sometimes morally decisive). This is because failures of planning predictably increase the harms for which a state is responsible, either by allowing preventable harms to occur or by leaving unavoidable harms uncompensated. Postwar reconstruction is a complex and difficult undertaking. It requires securing funding, coordinating agencies and allies, building up administrative and logistical capacities, and so forth. All of this takes time, as was so disastrously and notoriously demonstrated in the early U.S. experience in Iraq, where the Bush administration allotted a mere sixty days to prepare for the reconstruction of a country of 26 million.

The morality of the postwar (jus post bellum) is not detached and downstream of jus ad bellum in the way the traditional framework suggests. Prospects for postwar mitigation and compensation feed directly into ad bellum proportionality. Thus, the failure to improve those prospects by advanced planning does not merely set a nation up to fail to do justice after the war, but to misjudge whether the war should be waged at all.

David Clark is an Assistant Professor of Philosophy at the University of Arizona. His research interests range across issues in moral, legal, and political philosophy, many of which gravitate around questions about harm: when it may be inflicted, how it should be distributed, and who must bear the costs of repairing it.

Disclaimer: Any views or opinions expressed on The Public Ethics Blog are solely those of the post author(s) and not The Stockholm Centre for the Ethics of War and Peace, Stockholm University, the Wallenberg Foundation, or the staff of those organisations.