Conversation so far:
What was the importance of bison to the peoples of the Blackfoot Confederacy?
Historically, the member peoples of the Blackfoot Confederacy were nomadic bison hunters and trout fishermen.
How did the peoples of the Blackfoot Confederacy hunt bison?
The hunters of the Blackfoot Confederacy would round up the buffalo into V-shaped pens, and drive them over a cliff.

Question: Why would they drive them over a cliff?
Self-contained rewrite: Why would the hunters of the Blackfoot Confederacy drive the bison over a cliff?