Wars are large-scale armed conflicts between two or more organized groups. The basic problem of warfare is that it involves inflicting death and suffering on people, who, in ordinary circumstances, would have fundamental rights that protect them against being treated in these ways. Of course, everyone recognizes that wars are problematic in other respects: they corrupt and destroy institutions and relationships, they waste vast sums of wealth that could be used to remedy entrenched vulnerability, and they cause irreversible and massive damage to the natural environment. These are by no means negligible costs. And yet when considering the ethics of war, most start with the killing and the suffering, because if the killing cannot be justified, then the rest is irrelevant: our only choice is to affirm pacifism. However, justifying the killing is a necessary, but not a sufficient condition of justifying wars as a whole. There remain important questions to be asked about how and why the killing may be done. While the permissibility of killing per se provides the philosophical foundations of any theory of just war, the superstructure requires attention to specific questions governing the practice of warfare. In particular, for what reasons may conflict be permissibly initiated? How can we fight permissibly? How can we end wars, and deal with their aftermath, permissibly? The first two—justified resort and justified conduct—correspond to jus ad bellum and jus in bello in historical just war theory. The third is a more novel, less-discussed contribution, coined as jus post bellum by recent scholars. Only a war in which the killing is justified, and which is started, fought, and ended justifiably, can properly be called a just war.
Jus Post Bellum in Just War Theory