The Caroline affair (also known as the Caroline case) is a diplomatic crisis beginning in 1837 involving the United States, Britain, and the Canadian independence movement
It begins in 1837 when William Lyon Mackenzie and other Canadian rebels commanding the ship Caroline flee to an island in the Niagara River, with support from nearby American citizens.
British forces then board the ship, kill an American crew member in the fighting, then burn the ship and send it over Niagara Falls.
This action outrages the United States.
In retaliation, a group of American and Canadian raiders attack a British ship and destroy it.
There are several other attacks in 1838 between the British and Americans.
The diplomatic crisis is defused by the negotiations that lead to the Webster-Ashburton Treaty in 1842, where both the Americans and British admit to wrongdoing.
In the aftermath, the incident leads to the legal principle of the Caroline test.
The principle states that the necessity for [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.
