Native American Culture varied drastically from tribe. What was the cause for these drastic changes in culture

The U. S. government's policies towards Native Americans in the second half of the nineteenth century were influenced by the desire to expand westward into territories occupied by these Native American tribes. By the 1850s nearly all Native American tribes, roughly 360,000 in number, lived to the west of the Mississippi River. These American Indians, some from the Northwestern and Southeastern territories, were confined to Indian Territory located in present day Oklahoma, while the Kiowa and Comanche Native American tribes shared the land of the Southern Plains.