Before the European Settlers came to the great plains of North America, the Native Americans lived in equilibrium with the buffalo herds. As head of a tribe you decide where your tribe (teepee) goes; the buffalos are moved by all players.
At the beginning of the game, the buffalos are placed on the marked areas. Your teepees are placed where you want to place them.
Game victory is yours when you have the most teepees at the end of the game.
But during the game you have to make sure that you maintain your teepees. And while the game progresses this gets harder and harder.
As long as you have buffalos near your teepees there is no problem, but it can occur that you fall behind with a teepee or that it gets isolated...
Each teepee that makes it to the end of the open plains is safe.