Final answer:
The U.S. government's assimilation policy in 1871 involved treating Native American tribes not as independent nations but as individuals, effectively ending the recognition of tribal sovereignty.
Step-by-step explanation:
In 1871, the U.S. government's policy aimed to assimilate American Indians into American society, which departed from earlier practices that somewhat recognized tribal sovereignty. This policy included not recognizing tribes as independent nations anymore and instead treating American Indians as individuals under U.S. law. As a result, tribes were not allowed to sign new treaties and were subjected to the laws of the United States, losing much of their sovereignty and the right to self-govern. The government's actions led to further displacement and assimilation of Native Americans.