Caroline affair

The Caroline affair (also known as the Caroline case) was a diplomatic crisis beginning in 1837 involving the United States, Britain, and the Canadian independence movement. It began in 1837 when William Lyon Mackenzie and other Canadian rebels, commanding the ship Caroline, fled to an island in the Niagara River, with support from nearby American citizens. British forces then boarded the ship, killed an American crew member in the fighting, and then burned the ship and sent it over Niagara Falls.

This action outraged the United States. In retaliations, a group of American and Canadian raiders attacked a British ship and destroyed it. There were several other attacks in 1838 between the British and Americans. The diplomatic crisis was defused by the negotiations that led to the Webster-Ashburton Treaty in 1842, where both the Americans and British admitted to wrongdoing.

In the aftermath, the incident led to the legal principle of the Caroline test. The principle states that the necessity for preemptive self-defense must be "instant, overwhelming, and leaving no choice of means, and no moment for deliberation", as formulated by Daniel Webster in his response to British claims that they attacked the Caroline in self-defense. The Caroline test remains accepted as part of international law today. In 2008, Thomas Nichols wrote:

The Reform Movement of Upper Canada (today's Ontario) was a movement to make the British colonial rule in Canada more democratic and less corrupt. William Lyon Mackenzie was one of the key leaders of this movement. He was repeatedly elected to serve in a hostile parliament that repeatedly ejected him for his reform efforts. By 1837, Mackenzie had given up on peaceful means for reform and began to prepare for an uprising.

In December 1837, Mackenzie began the Upper Canada Rebellion by fighting the British in the Battle of Montgomery's Tavern. Mackenzie's forces were seriously outnumbered and outgunned, and they were defeated in less than an hour. He also suffered another major defeat a few days later in London. After these defeats, Mackenzie fled to Navy Island in the Niagara River, which they declared the Republic of Canada, on board the vessel SS Caroline.

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