An act of the national legislature, in which a state of war is declared to exist between the United States and some other nation. This power is vested in Congress by the Constitution, Art. I. There is no form or ceremony necessary, except the passage of the act.
The public proclamation of the government of a state, by which it declares itself to be at war with a foreign power, and which forbids all and every one to aid or assist the common enemy. A manifesto stating the causes of the war is usually published, but war exists as soon as the act takes effect.
It was formerly usual to precede hostilities by a public declaration communicated to the enemy, and to send a herald to demand satisfaction, but that is not the practice of modern times. In some countries, e.g., England, the power of declaring war is vested in the king, but he has no power to raise men or money to carry it on, which renders the right almost nugatory.