The first fur-trading post, Fort Ramon, was founded in 1807 by Manuel Lisa at the confluence of the Bighorn and Yellowstone Rivers, between present-day Billings  and Miles City. Beaver, much sought for European fashions, was the major item of trade. Some Indian tribes, notably the Salish and Crow, maintained friendly relations with the white traders and trappers. The Blackfeet, who controlled the Missouri River area, were hostile to the Salish, Crow, and whites.
John Jacob Astor’s American Fur Company built Fort Union at the confluence of the Yellowstone and Missouri in 1829 and finally induced the Blackfeet to trade peacefully by dispatching a Blackfeet-speaking trapper to bring them to the fort for a conference. The Blackfeet complied. Four thousand beaver pelts were taken from the heart of the heavily defended Blackfeet territory by Astor’s trappers in 1838.
Fort Union and the American Fur Company soon ruled the Montana fur trade. As beavers were increasingly trapped out (and European fashion changed), trade continued in buffalo hides. By 1840 the era of the trapper and mountain man was over; almost three dozen trading forts had been built in Montana before the beaver was trapped to near extinction.