Declaration of War Law and Legal Definition

Declaration of war is a nation’s announcement that it is commencing war against another nation. It is the public proclamation of the government of a state, by which it declares itself to be at war with a foreign power.

In U.S. declaration of war is an act of national legislature, in which a state of war is declared to exist between U.S. and some other nation. This power is vested in congress by U.S. Constitution. For declaration of war no ceremony is necessary except passage of the act.