The Caroline Affair refers to a series of events beginning in 1837 that strained relations between the United States and Canada (and thus Great Britain).
A band of Canadian rebels, led by William Lyon Mackenzie, seeking a more democratic Canada, had been forced to flee to the United States after leading a failed rebellion in Upper Canada (now Ontario). They took refuge on Navy Island on the Canadian side of the Niagara River, which separates the two counties (between Ontario and New York). American sympathizers, who considered the rebellion a belated continuation of the American Revolutionary War, supplied them with money, provisions, and arms via the steamboat SS Caroline. On December 29, Canadian loyalist Colonel Sir Allan MacNab ordered a party of militia to cross the river and set the Caroline ablaze. Finding her docked at Fort Schlosser, New York, (near the current Power Authority intakes), they seized her, towed her into the current, set her afire and cast her adrift over Niagara Falls, killing one American (Amos Durfree) in the process.
It was reported that dozens of Americans were killed as they were trapped on board, although the ship had been abandoned before being set adrift. In response on May 29, 1838 American forces burned British steamer Sir Robert Peel while it was in the United States. The tensions were ultimately settled by the Webster-Ashburton Treaty. President Martin Van Buren sent General Winfield Scott to prevent further American incursions into Canada.
This incident has been used to establish the principle of "anticipatory self-defense" in international politics, which holds that military action may be justified by the mere threat of armed attack.
