 John Jacob Astor's American Fur Company took advantage of the law by opening a post in Prairie du Chien in 1817, and it soon became the dominant trading firm on the Upper Mississippi.Jean Joseph Rolette was the company's first agent in the city, and he built the warehouse circa 1828.In the 1820s and 1830s, the American Fur Company continued to control the Upper Mississippi fur trade and expanded its influence throughout the Louisiana Territory.