John Jacob Astor's American Fur Company built Fort Union Trading Post in 1828 near the junction of the Missouri and Yellowstone rivers in what is now North Dakota. In it's heyday, the post was a busy place and employed up to 100 people. It became the headquarters for trading buffalo hides and other furs with the Assiniboine, Crow, Cree, Ojibway, Blackfeet, and Hidatsa Tribes.

Fort Union Trading Post was established in 1828 by the American Fur Company. It was not a government or military post, but a business, established for the specific purpose of doing business with the Plains Indians. It lasted until 1867, making it the longest-lasting American fur trading post. At that time, it was purchased by the U S Army and torn down to provide building materials for the expansion of Fort Buford, a military post a few miles downstream.

With the help of local citizens and agencies, the site was acquired by the National Park Service in 1966. After three archaeological projects, reconstruction of the Bourgeius House was begun in 1987, followed by the walls and bastions and finishing with the Trade House in 1991.

Still considered an archaeological site, Fort Union protects the relics of a unique era of history that is brought to life in its reconstructed buildings.