Blackfoot refers specifically to a Native American group; it's a proper noun and should always be capitalized. The Blackfoot nation plays a significant role in North American history.
Pro Tip 2/3
Geographic Distribution
The Blackfoot people traditionally live in the Northwestern Plains of North America. In history class, we studied how the Blackfoot roamed vast areas of today's Montana.
Pro Tip 3/3
Tribal Association
Blackfoot refers to a collective identity; there can be individual tribes within it. The Blackfeet Tribe is one of the three Blackfoot confederacy tribes.