[BuckSkin]

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. For the United States, Article One, Section Eight of the Constitution says "Congress shall have power to ... declare War". The War Powers Resolution of 1973 (50 U.S.C. 1541–1548) was a United States Congress joint resolution providing that the President can send U.S. armed forces into action abroad only by authorization of Congress or if the United States is already under attack or serious threat. The War Powers Resolution requires the president to notify Congress within 48 hours of committing armed forces to military action and forbids armed forces from remaining for more than 60 days, with a further 30 day withdrawal period, without an authorization of the use of military force or a declaration of war. The resolution was passed by two-thirds of Congress, overriding a presidential veto.
With that said the United States has only declared war 5 times in it's entire history. Clinton set the precedent with Operation Desert Fox and his two successors have followed suit.