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?

Question: Where did they migrate from?
Self-contained rewrite: Where did the Niitsitapi migrate from?