Desire for Peltry.

The Trans-Mississippi commerce in animal pelts took three basic forms: the Upper Missouri River fur trade, the Rocky Mountain trapping system, and the independent trappers of the southern Rockies. Sent by President Thomas Jefferson, Meriwether Lewis and William Clark journeyed up the Missouri River to, among other things, discover the potential for an American fur trade in the recently acquired Louisiana Purchase. Reports of their expedition set off a flurry of American-based excursions into the northern plains. In 1807 Manuel Lisa established the first American trading post in Montana. There, Lisa and his men traded supplies for furs with natives.

American Fur Company.

By 1822 five leading fur companies worked the upper Missouri in hopes of profiting from sales in beaver skins. Only five years later John Jacob Astor's American Fur Company developed a virtual monopoly among American firms on the...