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About Declarations of War by Congress


The Constitution grants Congress the sole power to declare war. Congress has declared war on 11 occasions, including its first declaration of war with Great Britain in 1812. Congress approved its last formal declaration of war during World War II. Since that time it has agreed to resolutions authorizing the use of military force and continues to shape U.S. military policy through appropriations and oversight.

CountryDateSenate VoteEffective Date
Great Britain1812Jun 17, 181219-13Jun 18, 1812
Mexico1846May 12, 184640-2
Spain1898Apr 25, 1898UC
Germany1917Apr 4, 191782-6
Austria-Hungary1917Dec 7, 191774-0
Japan1941Dec 8, 194182-0
Germany1941Dec 11, 194188-0
Italy1941Dec 11, 194190-0
Bulgaria1942Jun 4, 194273-0
Hungary1942Jun 4, 194273-0
Rumania1942Jun 4, 194273-0