The correct answer is Option B) They United against Native American tribes.
Poeple moved to specific towns because they were united against the Native American tribes.
As the United States began to expand westwards, they encoursted lush landscapes with huge potential. However, all these places were already inhabited by numerous Native American tribes.
The government began to establish small towns in these places.
As more and more people heard about these prosperous areas, they began to converge and populate these towns.
The idea was to eventually drive the Native Americans out of their own land and use their abundant natural resources.