How Does the US Officially Declare War?

The United States has officially declared war 11 times in the nation’s history, the first time for the War of 1812 and most recently for World War II. According to the U.S. Constitution, Congress has the exclusive authority to declare war, but Congress has always exercised that power in response to a formal request from the president.

Since World War II, the U.S. has engaged in extended military conflicts in Korea, Vietnam, Afghanistan and Iraq, but none of those conflicts received an official declaration of war. Instead, Congress passed “authorizations for the use of military force” that allowed for the deployment of U.S. troops without requiring a full declaration of war.

Article I, Section 8, Clause 11 of the Constitution says that Congress has the power “To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water.” Although the founding document doesn’t lay out a formal procedure for declaring war, the president and Congress have followed the same process all 11 times that war has been declared:

For example, a day after Japan attacked Pearl Harbor, President Franklin D. Roosevelt addressed a joint session of Congress. Calling December 7, 1941, “a date which will live in infamy,” Roosevelt requested a formal declaration of war. “I ask that the Congress declare that since the unprovoked and dastardly attack by Japan on Sunday, December 7, 1941, a state of war has existed between the United States and the Japanese Empire.”

The Senate took up the matter immediately and within minutes passed a joint resolution declaring war on Japan by a vote of 82-0. The House followed with its own roll call vote of 388-1, and Roosevelt signed the war declaration the very same day, December 8.

The U.S. hasn’t issued an official declaration of war since 1942, when it declared war on five different Axis powers during World War II: Japan, Germany, Bulgaria, Hungary and Romania.

Instead, since World War II, Congress has mostly issued authorizations for use of military force (AUMFs) in place of declarations of war. It was AUMFs that authorized presidents to commit U.S. troops to the wars in Vietnam, the Persian Gulf, Afghanistan and Iraq as well as to conduct targeted strikes against various terrorist organizations and rogue states. (President Harry S. Truman characterized the Korean War as a “police action” that didn’t require a formal declaration of war from Congress.)

According to the War Powers Resolution of 1973, the president must submit a report to Congress within 48 hours of sending U.S. forces into “hostilities.” Congress then has 60 days to issue either a declaration of war or an AUMF. If Congress doesn’t give its authorization within 60 days, the president must withdraw the forces, with a possible 30-day extension for safe removal.

It’s not clear, however, whether the president needs any kind of congressional approval for taking military action. The Constitution gives Congress the sole power to “declare war,” but Article II, Section 2 also names the president “Commander in Chief of the Army and Navy of the United States.” Lawyers for the executive branch have questioned the constitutionality of the War Powers Resolution, arguing that presidents can take any military action they please as long as it doesn’t rise to the level of “war in the constitutional sense.”

The issue of the scope of the president’s war powers is a matter of ongoing debate and has not been settled by the Supreme Court.