Just War Theory

The principle that war is sometimes necessary and morally justifiable. The just war theory is the most universally recognized moral concept for evaluating the use of force. It has developed from a complex, varied heritage built on layers of philosophical, religious, historical, and social precepts. The theory's foundations lie in Christian beliefs and natural law, which subsequent secular philosophers and historical traditions and documents have interpreted and codified.

History of the Just War Theory

The early church father St. Augustine of Hippo is generally acknowledged as the first to present a thorough and critical analysis of warfare as a legitimate tool of the state. Writing in the fourth century CE, St. Augustine asserted that a just war may be preferable to an unjust peace. Using biblical references, he maintained that necessity sometimes requires the use of force in a nation's life, claiming that it is ordained by natural law.

For St. Augustine, a just war, or justum bellum, had to be fought for the right reasons and waged through rightful authority. The only justification for war could be a desire for promulgating and establishing peace, and such a war could be waged only by a recognized leader.

Centuries later, in the 13th century CE, Saint Thomas Aquinas, in his work the Summa Theologica, formulized many of the principles that St. Augustine had asserted. Aquinas developed and presented what became the just war theory. He developed justifications for war and the kinds of activities that are permissible in war. The requirements for a just war, as [Page 401]laid out by Aquinas, included the following: the ruler commanding the war must possess the lawful authority to wage war, a just cause must exist, and those waging war must have the right intention of promoting good and avoiding evil. The lawful authority to wage war remains with the sovereign; private persons must vindicate their rights through the ruling power.

The Renaissance scholar Hugo Grotius, who is sometimes referred to as the father of international law, is credited with secularizing just war theory. His book On the Rights of War and Peace, published in 1625, examines the rights of nations to use self defense. Grotius established three basic criteria for a war to be considered just—the danger faced by the nation must be immediate, the force used must be necessary to adequately defend the nation's interests, and the use of force must be proportional to the threatened danger. Based on the writing of Grotius, the concepts of just war began to be institutionalized at an international level as these principles began to transcend the legal codes of individual nations.

Following Grotius, other historical developments furthered the transformation of just war theory into international law. The Hague Conventions, beginning in 1899, codified the just war theory. Then, following World War II, the Nuremburg Tribunal established just war theory as universally binding and customary law, and the Charter of the United Nations recognized each sovereign nation's inherent right to self-defense.

Contemporary Thought

Contemporary theorists separate the commonly recognized elements of just war theory in a two-part classification that distinguishes between the rules that govern the justice of war (jus ad bellum) from those that govern just and fair conduct in war (jus in bello). A number of moral requirements have evolved as the principles of the justice of war. Such a war must have a just cause, be declared by a proper authority, possess the right intention, have a reasonable chance of success, and have an end that is proportional to the means used.

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