When Has Congress Declared War? Hill hasn't formally declared war since 1942 By Matt Cantor, Newser User Posted Sep 2, 2013 9:55 AM CDT Updated Sep 2, 2013 10:33 AM CDT 46 comments Comments Congress hasn't formally declared war since 1942. (Shutterstock) (Newser) – With President Obama turning to Congress for a decision on Syria, BuzzFeed offers a quick Hill history lesson. Congress hasn't formally declared war since 1942, the site notes. But before that, it wasn't such a rare move: Congress backed war against Britain in 1812, by way of a joint resolution that passed the Senate 19-13. The conflict was fueled by trade and other disagreements following the American Revolution. Congress declared war on Mexico in 1846 amid border conflicts; Mexico surrendered the following year, and the southwestern US expanded quite a bit. Capitol Hill declared war on Spain in 1898 following the explosion of the USS Maine, sent to protect US interests in a volatile Cuba. War with Germany was declared in 1917 after evidence emerged that Germany planned to help Mexico regain southwestern US territories. And in 1941, after Pearl Harbor, a unanimous Senate backed war with Japan, Germany, and Italy; the next year, it was Bulgaria, Hungary, and "Rumania." Head to BuzzFeed for the full, illustrated story.