Wars fought to redress grievous wrongs or put a stop to evil have been termed "just wars." The concept has its origins in classical and theological philosophy and was explicit in the Christian ethics of Saint Augustine. Just war theory describes narrow circumstances and tight constraints on the ends and means that are required to apply this term. Although Western law has slowly come to accept war as an inevitable instrument of national policy and turned its attention to setting standards for the conduct of war, important echoes of just war theory remain. A distinction was made at Nuremberg, and later embedded in articles 2 and 51 of the United Nations charter, between unacceptable aggressive war and acceptable wars of self defence. Contemporary arguments about particular wars still rely on the seven main principles of just war theory. Application of these principles to the conflict in Afghanistan does not settle the debate but it might help to structure the discussion.