Conversation so far:
What can you tell me about the early history of Blackfoot Confederacy?
The Niitsitapi, also known as the Blackfoot or Blackfeet Indians, reside in the Great Plains of Montana and the Canadian provinces of Alberta and Saskatchewan.
When did the Niitsitapi reside in the Great Plains?
Where did the Niitsitapi migrate from?
Due to language and cultural patterns, anthropologists believe the Niitsitapi did not originate in the Great Plains of the Midwest, but migrated from the upper Northeastern part of the country.
How did the Niitsitapi adapt to being in the plains?
Adopting the use of the horse, the Niitsitapi established themselves as one of the most powerful Indian tribes on the Plains in the late 18th century.
What kind of resources did the Niitsitapi have in their early history on the plains?
The Niitsitapi main source of food on the plains was the American bison.

Question: What other tribes were they associated with?
Self-contained rewrite: What other tribes were the Blackfoot Confederacy associated with?