Montana's early white settlers developed a small network of forts used as trading posts. These sites were visited by hired fur traders, local Indian traders, early missionaries arriving to convert and assimilate American Indians, and others looking to acquire supplies and exchange news. One of the earliest examples was Fort Benton, built by the Chouteau brothers—Western Agents for John Jacob Astor's American Fur Company—and positioned at a port on the Missouri River to facilitate trade by riverboat.
After the American Civil War, the US Army purchased old forts and constructed new ones to protect and support growing numbers of white settlers moving into the Montana Territory. These forts were stops along trails, like the Bozeman Trail, used for early Gold Rush travel. As the US Army focused its attention increasingly on the West and its containment of American Indian tribes on reservations, these forts provided supplies and housing for divisions of soldiers fighting in the Indian Wars, including divisions made up of African Americans known as Buffalo Soldiers.
Particularly after the dramatic US Army defeat at the Battle of Little Bighorn in 1876, and despite the fact that many Indians were already living on reservations, the US Army created new outposts like Fort Custer, Fort Keogh, and Fort Ellis to protect settlers from real and imagined Indian threats. These forts also provided jumping-off points for military exploration into surrounding unsettled areas like present-day Yellowstone National Park. Many of the military forts were decommissioned around the 1880s with the arrival of the railroad, while others were absorbed into Indian reservations.