<P> The last time the United States declared war on any nation was in 1942, when war was declared against Axis - allied Hungary, Bulgaria, and Romania, because President Franklin Roosevelt thought it was improper to engage in hostilities against a country without a declaration of war . Since then, every American president has used military force without a declaration of war . </P> <P> This article will use the term "formal declaration of war" to mean Congressional legislation that uses the phrase "declaration of war" in the title . Elsewhere, this article will use the terms "authorized by Congress", "funded by Congress" or "undeclared war" to describe other such conflicts . </P> <P> The United States has formally declared war against foreign nations five separate times, each upon prior request by the President of the United States . Four of those five declarations came after hostilities had begun . James Madison reported that in the Federal Convention of 1787, the phrase "make war" was changed to "declare war" in order to leave to the Executive the power to repel sudden attacks but not to commence war without the explicit approval of Congress . Debate continues as to the legal extent of the President's authority in this regard . Public opposition to American involvement in foreign wars, particularly during the 1930s, was expressed as support for a Constitutional Amendment that would require a national referendum on a declaration of war . Several Constitutional Amendments, such as the Ludlow Amendment, have been proposed that would require a national referendum on a declaration of war . </P> <P> After Congress repealed the Gulf of Tonkin Resolution in January 1971 and President Richard Nixon continued to wage war in Vietnam, Congress passed the War Powers Resolution (Pub. L. 93--148) over the veto of Nixon in an attempt to rein in some of the president's claimed powers . The War Powers Resolution proscribes the only power of the president to wage war which is recognized by Congress . </P>

Congress has formally declared war times in u.s. history