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.
| Country | Date | Senate Vote | Effective Date |
|---|---|---|---|
| Great Britain | 1812 Jun 17, 1812 | 19-13 | Jun 18, 1812 |
| Mexico | 1846 May 12, 1846 | 40-2 | — |
| Spain | 1898 Apr 25, 1898 | UC | — |
| Germany | 1917 Apr 4, 1917 | 82-6 | — |
| Austria-Hungary | 1917 Dec 7, 1917 | 74-0 | — |
| Japan | 19411208 Dec 8, 1941 | 82-0 | — |
| Germany | 19411211 Dec 11, 1941 | 88-0 | — |
| Italy | 19411211 Dec 11, 1941 | 90-0 | — |
| Bulgaria | 1942 Jun 4, 1942 | 73-0 | — |
| Hungary | 1942 Jun 4, 1942 | 73-0 | — |
| Rumania | 1942 Jun 4, 1942 | 73-0 | — |
Information provided by the Senate Historical Office.
