Abstract

The international law regulating resort to armed force, still known by the Latin phrase, the jus ad bellum, forms a principal substantive subfield of international law, along with human rights law, international environmental law, and international economic law. Among theologians, philosophers, and political scientists, just war theory is a major topic of study. Nevertheless, only a minority of scholars and practitioners know both jus ad bellum and just war theory well. Lack of knowledge has led to the erroneous view that the two areas are in conflict. This article responds to this misapprehension, explaining the deep compatibility of international law and just war theory. Today's jus ad bellum, especially the peremptory norm against aggression, is not only the law; it also forms the minimum threshold of a just war under just war theory. In other words, for a war to be morally just, it must at least be lawful. To go to war in violation of the jus ad bellum is both a legal and a moral wrong. Compliance not only fulfills the general moral good of obedience to law; it forms the first step toward fulfilling moral obligations in the grave area of war. This characterization of the relationship between law and morality is seen in the history of the legal prohibition on force and in the actual set of rules that make up the contemporary regime. Comprehensive and persuasive accounts of the jus ad bellum and just war theory consistently reflect this thesis.