What was the last conflict for which the U.S. Congress declared war?

The last conflict for which the U.S. Congress formally declared war was World War II. This declaration, made on December 8, 1941, followed the surprise attack on Pearl Harbor by Japan. Following this declaration, the U.S. engaged in a multi-theater war that involved significant military mobilization and substantial global military engagement.

Subsequent conflicts, such as the Korean War, Vietnam War, and Gulf War, did not involve formal declarations of war. Instead, these conflicts were often initiated through other forms of congressional authorization, resolutions, or presidential assessments of national security needs, which do not carry the same legal weight or requirements as a formal declaration of war. This distinction is crucial in understanding how military actions are authorized and the power dynamics between Congress and the president in war-making decisions.