[65] Monroe had long worked for peace with the British, but he came to favor war with Britain, joining with "war hawks" such as Speaker of the House Henry Clay. With the support of Monroe and Clay, Madison asked Congress to declare war upon the British, and Congress complied on June 18, 1812, thus beginning the War of 1812.[66]
The war went very badly, and the Madison administration quickly sought peace, but were rejected by the British.[67] The U.S. Navy did experience several successes after Monroe convinced Madison to allow the Navy's ships to set sail rather than remaining in port for the duration of the war.[68] After the resignation of Secretary of War William Eustis, Madison asked Monroe to serve in dual roles as Secretary of State and Secretary of War, but opposition from the Senate limited Monroe to serving as acting Secretary of War until Brigadier General John Armstrong won Senate confirmation.[69] Monroe and Armstrong clashed over war policy, and Armstrong blocked Monroe's hopes of being appointed to lead an invasion of Canada.