From the outbreak of war with Napoleonic France, Britain had enforced a naval blockade to choke off neutral trade to France, which the US contested as illegal under international law. To man the blockade, Britain impressed American merchant sailors into the Royal Navy. Incidents such as the Chesapeake–Leopard affair, which happened five years before the war, inflamed anti-British sentiment in the US. In 1811, the British were in turn outraged by the Little Belt affair, in which 11 British sailors died. Britain supplied Indians who raided American settlers on the frontier, hindering American expansion and provoking resentment.Historians debate whether the desire to annex some or all of British North America (Canada) contributed to the American decision to go to war. On June 18, 1812, US President James Madison, after heavy pressure from the War Hawks in Congress, signed the American declaration of war into law.