A group of Canadian rebels, led by William Lyon Mackenzie, seeking a Canadian republic, had been forced to flee to the United States after leading the failed Upper Canada Rebellion in Upper Canada (now Ontario). They took refuge on Navy Island on the Canadian side of the Niagara River, which separates the two countries (between Ontario and New York) and declared themselves the Republic of Canada under MacKenzie's "general" Rensselaer Van Rensselaer (nephew of General Stephen Van Rensselaer). American sympathizers supplied them with money, provisions, and arms via the steamboat SS Caroline.