Act of War

A casus belli is an act or event that provokes or is used to justify a war. It involves direct offenses or threats against the nation declaring war, or offenses or threats against its ally under a mutual defense pact. The term originated in Europe in the 17th and 18th centuries through the writings of Hugo Grotius, Cornelius van Bynkershoek, and Jean-Jacques Burlamaqui, and is used to describe the case for war given before the term came into wide use. A government typically lays out its reasons for going to war, its intended means of prosecuting the war, and the steps that others might take to dissuade it from going to war. Modern international law recognizes at least three lawful justifications for waging war: self-defense, defense of an ally required by the terms of a treaty, and approval by the United Nations.learn more on wikipedia