On April 2, 1917, President Woodrow Wilson asked a special joint session of the United States Congress for a declaration of war against the German Empire. Congress responded with the declaration on April 6.

A declaration of war is a formal declaration issued by a national government indicating that a state of war exists between that nation and another. A document by the Federation of American Scientists gives an extensive listing and summary of statutes which are automatically engaged upon the United States declaring war.