The increase in violence between white settlers and Plains Indians most directly resulted from a nativist theories that were used to justify violent actions. b the competition for western land and the resources it provided. c the attempt by the federal government to assimilate Native Americans into the dominant culture. d the destruction of the buffalo by white settlers moving into the western territories.

. b the competition for western land and the resources it provided.

Explanation:

Given white settlers on American soil decided to exploit the land in America to their satisfaction, including mining, etc, However, the native Americans are known to use their forest as a means of hunting games. This shows disagreement in the utilization of the land between the two, and often lead to war.

It can be said that the increase in violence between white settlers and Plains Indians most directly resulted from "the competition for western land and the resources it provided.":

the constitution gives congress the power to regulate commerce "among" the several states.