How did railroads help to “conquer the West?”

(a.)Their expansion convinced Jefferson that Louisiana would be a good purchase.

(b.)They were used by the first group of Americans to travel west of the Rocky Mountains.

(c.)They connected the country by moving people and goods across great distances.

(d.)They were a platform the United States military used to conquer and control Indian tribes.

I hope this can some what help..

Explanation:

it's either c or d

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.

definitely a for sure. ill see and update if i get the answer