JUST WAR

medieval European concept that a ruler, by proper declaration and with proper motives, might employ armed force outside his normal jurisdiction to defend rights, rectify wrongs, and punish crimes. He could, that is, take up arms for a just cause (which in practice was interpreted according to one's own lights). The concept developed as early as St. Augustine in the 4th century and was still accepted by the Dutch jurist and writer on international law Hugo Grotius in the 17th. Its popularity thereafter declined, though in the 20th century it enjoyed a revival in somewhat new form, with the idea that a nation might resort to armed force in self-defense or in the execution of collective obligations toward international peace-keeping operations.