There would be two answers for this question. For the reasons that it could give people an idea of what cause the regional conflict taking place and it also influences the region's political and economic decisions. Furthermore, understanding the people on both of these regions would give us a keen understanding on how they are different from us.
The answer is: to keep the population isolated from freer societies.
Development of more railroad systems contributed
most to US westward expansion in the second half of the nineteenth century.
The correct answer between all the choices given is the second choice or
letter B. I am hoping that this answer has satisfied your query and it will be
able to help you in your endeavor, and if you would like, feel free to ask
another question.