How did the following contribute to the end of the Western and Plain Indians' traditional way of life:
1)the establishment of reservations
2)the white and black Americans' westward movement
3)American perception of private ownership of property versus tribal ownership of land
I would argue that the chain of causation here works from the bottom up. That is, I think that your Factor #3 helped cause Factor #2, which helped cause Factor #1. Factor #1 (the establishment of reservations) essentially ended the traditional way of life for the Plains Indians.
Historians typically argue that Americans believed in the idea of private property where the Native Americans did not. Americans clearly believed that individual people had the right and the ability to own parcels of land. Historians say that Native Americans did not have this concept. They say that the Indians believed in tribal ownership, not individual ownership. They also say that the Indians did not have the idea of owning land in a way that could prevent others from using it. This meant that the Indians did not understand the treaties they made in the same way the whites did. The whites believed the Indians were agreeing that they would give up any right to use the land in question while the Native Americans did not believe any such thing. Thus the Native Americans lost the right to use their land without realizing what they were agreeing to.
Once the land was bought/taken from the Indians, westward movement became more possible. The land could be given to the homesteaders and others. This, of course, meant that it would be even more difficult for the Native Americans to use that land.
Eventually, the pressure from the westward movement induced the government to force the Indians onto reservations. When the Indians were forced onto the reservations, their traditional way of life was essentially over. They were no longer able to roam nomadically as they once did. Even if they could have roamed, the westward movement had killed off the herds of bison on which the Natives had lived. In these ways, the factors that you mention led to the destruction of the Native Americans’ traditional way of life.