Fort Mackinac (pronounced: MACK-in-awe) is a former British and American military outpost garrisoned from the late 18th century to the late 19th century in the city of Mackinac Island, Michigan, on Mackinac Island. The British built the fort during the American Revolutionary War to control the strategic Straits of Mackinac between Lake Michigan and Lake Huron, and by extension the fur trade on the Great Lakes. The British did not relinquish the fort until fifteen years after American independence.