Fort Mackinac (on the island) was founded during the American Revolution. Believing Fort Michilimackinac on the mainland was too vulnerable to American attack, the British moved the fort to Mackinac Island in 1780. Americans took control in 1796. In 1812, in the first land engagement of the War of 1812, the British captured the fort. In a bloody battle in 1814 the Americans attempted but failed to retake the fort. It was returned to the United States after the war. The fort remained active until 1895. During these years Mackinac Island was transformed from a center of the fur trade into a major summer resort.
And there you have it.