There were two main types of policy that the US government conducted with respect to the Native American populations in the later 19th century. One was aggressive and military. The other did not involve the military and was oriented towards social changes.
Americans typically are more aware of the first set of policies. These were the policies behind the Indian Wars of the 1860s, ‘70s, and ‘80s. In this set of policies, the American government was trying to clear the Indians from lands that were desired by American settlers. Indians who refused to be moved onto reservations were pursued by the military, which attempted to force them to accede to the wishes of the government. These actions led to military conflict in many cases.
Fewer Americans are as aware of the other part of government policy towards Indians. This was the policy of assimilation. Once the Indians were on reservations, the government tried various policies to try to change Native Americans culturally. These included such things as the Dawes Severalty Act, which was meant to cause Indians to live as individual farmers. There was also the use of boarding schools to try to eradicate Indian culture and instill American ways.
These two policies were very different, but both were part of American policy towards Indians in the later 1800s.