For a time it seemed that the company had been destroyed, but following the war the United States passed a law excluding foreign traders from operating on U.S. territory. This freed the American Fur Company from its competition with the Canadian and British companies, and ensured a monopoly for the American Fur Company in the Great Lakes region and the Midwest. In the 1820s the company expanded its monopoly into the Great Plains and the Rocky Mountains. To maintain control of the industry, smaller competitors were bought out or destroyed by the American Fur Company's ruthless business tactics. By 1830, the company had nearly complete control of the fur trade in the United States.
The company's time at the top of America's business world was short lived. Sensing the eventual decline of fur's popularity in fashion, John Jacob Astor withdrew from the company in 1834. The company split up, and the Pacific Fur Company became independent. The midwestern outfit would continue to be called the American Fur Company, and was now led by Ramsey Crooks. To cut down on expenses, the company began closing many of its trading posts.
Through the 1830s, competition began to resurface. At the same time, the availability of furs in the Midwest declined. Hudson's Bay Company, from its Columbia District headquarters at Fort Vancouver began an effort to destroy the American fur companies during the late 1830s. By depleting furs in the Snake River country and underselling the American Fur Company at the annual Rocky Mountain Rendezvous, the HBC effectively destroyed American fur trading efforts in the Rocky Mountains. By the 1840s, silk was replacing fur as the clothing fashion in Europe. The company was unable to cope with all these factors. Despite efforts to increase profits by diversifying into other industries like lead mining, the American Fur Company folded. The assets of the company were split into several smaller operations, most of which failed by the 1850s.
On the frontier, the American Fur Company opened the way for the settlement and economic development of the Midwestern and Western United States. Mountain men working for the company carved the trails that led settlers into the West. Many cities in the Midwest and West, such as Astoria, Oregon, grew up around American Fur Company trading posts. The American Fur Company played a major role in the development and expansion of the young United States.