Final answer:
The Dawes Severalty Act of 1887 allowed the US to seize 90 million acres of Native American lands, allocating portions to individuals and selling the remainder, thereby undermining tribal sovereignty and promoting assimilation.
Step-by-step explanation:
In 1887, the United States government passed the Dawes Severalty Act which fragmented tribal lands, allocating parcels to individual Native American families while declaring the remaining tribal lands available for white settlement. Under this act, the President was authorized to distribute 160 acres of land to each Native American head of family, to be held in trust for 25 years before granting them full ownership and citizenship. The act profoundly impacted Native American society by drastically reducing their communal tribal lands and promoting assimilation into American society, ultimately resulting in Native Americans losing control over 90 million acres of their ancestral lands.