When white traders and settlers arrived in the region in the early 1800s, they did not find a land peopled with indigenous native tribes. Instead, the Indians of Montana were only recent immigrants, attempting to establish homelands and work out the cultural changes that their recent uprooting had caused. These tribes had been displaced as European settlement along the East Coast and in the Southwest increasingly forced Native American inhabitants from their traditional homelands, and they in turn displaced other tribes as all were forced north and west.

Some of the tribes that migrated to Montana during this period were not traditionally nomadic. Most came from woodlands in the Great Lakes–Mississippi Basin region, where they were sedentary, sometimes agricultural people who lived in permanent earthen dwellings. During the process of dislocation to the West, agriculture was lost and a hunting culture developed. The earth lodge was abandoned for the tepee. For these people, the buffalo became more than a food source: It was the central assumption on which their entire cultural life was predicated. Social organization was structured by warrior societies, and in some cases, by clan. Women were responsible for most of the daily work, save hunting and fighting. The Plains Indians shared an animistic religion.

The first tribe to enter Montana during the historic period was the Shoshone, who began to move into the southwestern corner of the state from the Great Basin area about 1600. They drove the resident Salish tribes (who had migrated from the Pacific Northwest several centuries earlier) farther north into the mountains. The Shoshone were fearsome warriors and the first Montana tribe to ride horses, which they had procured from the Spanish colonies.

The Crow Indians arrived in Montana shortly thereafter and settled along the Yellowstone River drainages, the first tribe to actually settle on the Montana prairies. The Blackfeet entered Montana from the north and east about a century later, around 1730, and brought the rifle. The Blackfeet, and their allies the Gros Ventre and the Assiniboin, soon established dominance over the northern Montana plains.

Further pressure from white settlement forced the Sioux and Northern Cheyenne into eastern Montana. The Cree and Chippewa tribes entered Montana in the 1870s as they were displaced from the Canadian prairies. As more and more tribes were squeezed into the area that would later become Montana, intertribal rivalries intensified. The Crow were hated enemies of the Blackfeet. The Blackfeet slaughtered the Salish or Kootenai Indians who dared to leave the safety of the mountains. As the Sioux entered Montana, they too became enemies of the Crow.

The Salish and Kootenai retained some traditions of the Northwest Indian tribes. Although these tribes once traveled over the Rockies to hunt buffalo, the presence of the fierce Blackfeet confederation on the prairies soon made these hunting expeditions too dangerous.