The Dawes Act (sometimes called the Dawes Severalty Act or General Allotment Act), passed in 1887 under President Grover Cleveland, allowed the federal government to break up tribal lands.
The federal government aimed to assimilate Native Americans into mainstream US society by encouraging them towards farming and agriculture, which meant dividing tribal lands into individual plots.
Only the Native Americans who accepted the division of tribal lands were allowed to become US citizens. This ended in the government stripping over 90 million acres of tribal land from Native Americans, then selling that land to non-native US citizens.