How did policymakers hope the policy of assimilation would work

They hoped the Indians would mingle with the white culture after the buffalo died.

Explanation:

Assimilation is the process by which individuals or social groups acquire cultural elements from other social groups or countries. This is the case, for example, with immigrant communities established in the host countries and absorbing the dominant culture. This process also occurred with the colonized peoples who were forced to absorb the dominant culture of the colonizing countries, thus losing much of their original culture. Therefore, in a more simplistic sense, assimilation consists in the learning of another culture.

In relation to assimilationist politics, it is said that it refers to the set of laws, political-administrative measures and social practices carried out by the Portuguese colonial government and Spanish to force the Indians to abandon their cultural traits and assimilate the culture Portuguese or Spanish and thus become Portuguese or Spanish citizens.

They were hoping that Indians would blend into white culture after the buffalo died off.