Before the 1850s the United States was divided in half with the western half set aside for Native Americans. However, around the mid-1850s Americans began to move west into these lands causing conflict. To settle the conflicts the government decided it was best to isolate Natives on to their own land where they would be protected. The idea was, and had been since Indian removal, that if Whites and Indians lived on the same land they would fight, and the Indians would lose. To protect them the government created large tracts of land they called reservations. Natives were told if they stayed on their land the government would supply them with food and would punish any whites that came on their land. Of course, the story of the west is white encroachment and the government continuously shrinking the size of the reservations.
Historically Speaking 