History of Native Americans

In the videos, History of Native Americans, what key issues were given for the fall of the Indian nations? https://www.screencast.com/t/RZkZkp6p4oj https://www.screencast.com/t/l1ABmnsWil https://www.screencast.com/t/Z949Iraf https://www.screencast.com/t/pSxBvR0e