Setting the scene
The War of 1812 was declared by the United States against Britain on June 18, 1812, the result of multiple grievances. Britain, at war with Napoleonic France, had imposed blockades and Orders in Council restricting American trade with Europe, and the Royal Navy impressed (kidnapped) an estimated 6,000-9,000 American sailors, claiming they were British deserters. Western 'War Hawks' like Henry Clay also coveted Canada and believed Britain was arming Native Americans to block U.S. expansion.
What happened
President James Madison, under pressure from War Hawks, asked Congress for war. The vote was close—79-49 in the House, 19-13 in the Senate—reflecting opposition from New England Federalists who depended on trade with Britain. The U.S. strategy was to invade Canada while Britain was distracted in Europe, assuming Canadians would welcome 'liberation.' The war went badly at first—American invasions of Canada in 1812-1813 failed, and the British blockade strangled American commerce. In 1814, after Napoleon's abdication, Britain sent veterans to America, burning Washington, D.C., in August 1814.
Why it still matters
The war ended with the Treaty of Ghent (December 24, 1814), which restored prewar boundaries—essentially a draw. But the Battle of New Orleans (January 8, 1815), fought after the treaty was signed but before news arrived, was a huge American victory that made Andrew Jackson a hero. The war had important consequences: it ended the Federalist Party, which had opposed the war; it spurred American manufacturing due to the blockade; it broke Native American power in the Old Northwest after Tecumseh's death; and it fostered American nationalism. The war is remembered in the U.S. for the Star-Spangled Banner and in Canada as a successful defense against American invasion.
Background
It included the burning of Washington and New Orleans defense.