Why did the United States declare war on Britain in 1812?
The most loudly voiced grievance was British interference with American rights on the high seas. "Free Trade and Sailors' Rights" was a popular battle cry.
But if British harassment of American shipping was the primary motivation for war, why then did the pro-war majority in Congress come largely from the South, the West, and the frontier, and not from northeastern ship owners and sailors?
Northeastern Federalists regarded war with Britain as a grave mistake. The United States, they feared, could not hope to successfully challenge British supremacy on the seas and the government could not finance a war without bankrupting the country.
Southerners and westerners, in contrast, were eager to avenge British insults against American honor. Many westerners and southerners had their eye on expansion, viewing war as an opportunity to add Canada and Spanish-held Florida to the United States.
War with Britain also offered another incentive: the possibility of clearing western lands of Indians by removing the Indians' strongest ally--the British. In late 1811, General William Henry Harrison provoked a fight with an Indian alliance at Tippecanoe Creek in Indiana. Since British guns were found on the battlefield, many Americans concluded that Britain was responsible for the incident.
Weary of Jefferson and Madison's policy of economic coercion, voters swept 63 out of 142 representatives out of Congress in 1810 and replaced them with young Republicans that Federalists dubbed "War Hawks." Having grown up on tales of heroism during the American Revolution, second-generation Republicans were eager to prove their manhood in a "second war of independence."