Answer:
D. They united against Native American tribes.
Step-by-step explanation:
Some regions of the United States possessed a wealth of natural resources and seemed to be very prosperous to live in, however, these lands were already inhabited by the natives. When the United States expanded westward, many people moved to specific towns in that region, with the goal of driving out the native tribes from their territories and enriching themselves by exploiting the natural resources of those lands.