The best explanation for how the Dawes Act promoted assimilation of Indigenous people is: It divided Indigenous lands into family farms called allotments.
The Dawes Act of 1887 aimed to assimilate Native Americans into American society by transforming their communal landholdings into individual allotments. This encouraged a shift from traditional communal living to a more Western, individualistic farming lifestyle, which was seen as a way to integrate Indigenous people into American culture.