Just-war theory deals with the justification of how and why wars are fought. The justification can be either theoretical or historical. The theoretical aspect is concerned with ethically justifying war and forms of warfare. The historical aspect, or the “just war tradition” deals with the historical body of rules or agreements applied (or at least existing) in various wars across the ages. For instance international agreements such as the Geneva and Hague conventions are historical rules aimed at limiting certain kinds of warfare. It is the role of ethics to examine these institutional agreements for their philosophical coherence as well as to inquire into whether aspects of the conventions ought to be changed.

Three traditions of thought dominate the ethics of war and peace: Realism; Pacifism; and Just War Theory (and, through just war theory, International Law). Perhaps there are other possible perspectives but it seems that very few theories on the ethics of war succeed in resisting ultimate classification into one of these traditions. They are clearly hegemonic in this regard.