The correct answer is B) Americans began to settle along railroad tracks out in the West.
Improvements in transportation, like the development of railroads during the early to mid 1800's, allowed citizens to move West of the original 13 states. This era of westward expansion (also referred to as manifest destiny) was one in which the American federal government continued to gain more land in North America either through treaty or war. This resulted in the creation of a transcontinental railroad. This railroad allowed people to move out West to get extremely cheap land and to start their new lives in these newly created cities.
