A war is only just if it is fought for a reason that is justified, and that carries sufficient moral weight. The country that wishes to use military force must demonstrate that there is a just cause to do so.

What are the two justifications for a just war?

The criteria are split into two groups: "right to go to war" (jus ad bellum) and "right conduct in war" (jus in bello). The first group of criteria concerns the morality of going to war, and the second group of criteria concerns the moral conduct within war.

What are justifiable reasons for going to war?

Modern international law recognizes only three lawful justifications for waging war: self-defense, defense of an ally required by the terms of a treaty, and approval by the United Nations.