How did westward migration change the plains indians' way of life?

Many of the European-American settlers who migrated west into Plains Indian lands used that land for ranching and farming. They often fenced that land in, which prevented buffalo herds from being able to roam the plains to access the best grass for food. Many other settlers also hunted the buffalo to near extinction, mostly for their pelts. The loss of buffalo had a massive impact on Plains Indian life, as the buffalo was their top source of food and money. Furthermore, incoming settlers brought diseases that wiped out many Indian communities. 

This strife cause wars between the Plains Indians and the settlers, known generally as the Indian Wars. These wars ended in 1890, with the Massacre of Wounded Knee, in which the U.S. Army gunned down hundreds of unarmed Lakota men, women, and children.