How and why the Plains Indians were subdued and confined to Indian Reservations during the 1870s?

The Plains Indians were subdued and confined to reservations during the 1870s primarily due to U.S. government policies aimed at westward expansion and the settlement of lands by white settlers. The discovery of gold and the demand for land for agriculture and railroads intensified conflicts, leading to military campaigns against various tribes. The implementation of treaties, often broken or unjustly negotiated, forced many Plains Indians onto reservations, where they faced poverty, cultural disruption, and loss of their traditional lifestyles. This process reflected broader patterns of colonialism and the desire to assimilate Native populations into Euro-American society.