Caroline Affair: In 1837 a group of men led by William Lyon Mackenzie rebelled in Upper Canada (now Ontario), demanding a more democratic government. There was much sympathy for their cause in the United States, and a small steamer, the Caroline, owned by U.S. citizens, carried men and supplies from the U.S. side of the Niagara river to the Canadian rebels on Navy Island just above Niagara Falls. On the night of Dec. 29, 1837, a small group of British and Canadians loyal to the Upper Canadian government crossed the river to the U.S. side where the Caroline was moored, loosed her, set fire to her, and sent her over the falls. One American was killed in the incident. Americans on the border were aroused to intense anti-British feeling, and soldiers under Gen. Winfield Scott were rushed to the scene to prevent violent American action. The affair passed over, though it had an aftermath, when one of the men who had taken part in the attack boasted of that fact when he was in the United States and was arrested as a criminal. That matter, too, was smoothed over, but the Caroline Affair and the Aroostook War helped to make relations with Great Britain very tense in the years before the Webster-Ashburton Treaty.