At the same time, the French strengthened Fort Michilimackinac at the Straits of Mackinac to better control their lucrative fur-trading empire. By the mid-18th century, the French also occupied forts at present-day Niles and Sault Ste. Marie, though most of the rest of the region remained unsettled by Europeans. France offered free land in an effort to attract families to Detroit, which grew to 800 people in 1765, the largest city between Montreal and New Orleans.