When talking about Glacier (see below), it’s impossible not to mention the Blackfoot. The Blackfoot had a territory that stretched from the North Saskatchewan River along what is now Edmonton, Alberta in Canada, to the Yellowstone River of Montana in the United States, and from the Rocky Mountains and along the South Saskatchewan River, east past the Cypress Hills.
Fast forward a little bit…In 1896, the Blackfoot sold a large portion of their land to the American government with hopes of finding gold or copper, but found nothing. In 1910, the land they sold officially became known as Glacier National Park. Today, many of the Blackfoot live on reserves in Canada. About 8,500 live on the 1,500,000 acre Montana reservation.
Way more information here.