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 | Jun 17, 1812 | 19-13 | Jun 18, 1812 |
| Mexico | May 12, 1846 | 40-2 | — |
| Spain | Apr 25, 1898 | UC | — |
| Germany | Apr 4, 1917 | 82-6 | — |
| Austria-Hungary | Dec 7, 1917 | 74-0 | — |
| Japan | Dec 8, 1941 | 82-0 | — |
| Germany | Dec 11, 1941 | 88-0 | — |
| Italy | Dec 11, 1941 | 90-0 | — |
| Bulgaria | Jun 4, 1942 | 73-0 | — |
| Hungary | Jun 4, 1942 | 73-0 | — |
| Rumania | Jun 4, 1942 | 73-0 | — |
