
Unlike some of the other Indian Tribes that call Montana home today, the Assiniboine moved west on their own without a lot of pushing from other tribes or Europeans. They are also present on two Indian Reservations in the state today, the Fort Belknap Indian Reservation and the Fort Peck Indian Reservation.
Early Contact

The French had future contacts with them, and noted that they were situated primarily around Lake Winnipeg. There numbers were around 10,000 at that point, and they lived in peace with Cree in the area, and eagerly began trading with the Hudson’s Bay Company.
Sometime around the first mention of them and the first initial contact, the Assiniboine split into two groups: one that remained in the Lake Winnipeg area of Canada, and another that headed south toward the Great Plains.
Heading to the Plains

This group that moved west changed just like the other tribes that had moved west before them, becoming more nomadic as they hunted the buffalo, a major feature of all Plains Indians. Still, they weren’t free from the influences of white settlers, even if they weren’t meeting them all that often.
In 1781 a smallpox epidemic struck the area and devastated the tribes there. The Assiniboine were hit hard, and they were weakened. It would become a common theme for them when further epidemics struck again in 1836 and 1869, and each time the tribe was weakened further, and their ability to defend themselves against other tribes decreased.
Not One to Mess With

This martial spirit preceded them, and when Lewis and Clark were coming back from Fort Clatsop on the Pacific Coast, they heard disconcerting rumors about a dangerous and deadly tribe called the Assiniboine that they’d do best to steer clear from. They were convinced that contact with the Assiniboine would be bad, and were thankful when they made it through without spotting them.
Notes
Miller, David; Smith, Dennis; McGeshick, Joseph R.; Shanley, James; Shields, Caleb. The History of the Assiniboine and Sioux Tribes of the Fort Peck Indian Reservation, Montana, 1800-2000. Fort Peck Community College: Poplar, 2008. p. 13-22.
Bryan, William L. Montana’s Indians: Yesterday and Today. American & World Geographic Publishing: Helena, 1996. p. 44.
Learn More about the Assiniboine
http://www.fortpecktribes.org/
National Museum of the American Indian
http://nmai.si.edu/home/