A U.S. law in 1816 excluded British traders from the United States, and many British fur traders who had helped to build the Old Northwest were compelled to become U.S. citizens and were reluctant to comply. The trade in the United States was now pushing west ahead of the advancing line of settlement, and the rich fur territories of the upper Missouri River, which had been tapped earlier by such traders as Manuel Lisa and Andrew Henry, attracted attention. After the first expedition of William Henry Ashley in 1823, the now celebrated mountain men (chief among them Kit Carson, Jedediah Smith, James Bridger, and Thomas Fitzpatrick), who were trappers more than they were traders, made the Rocky Mt. West known.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.