Why did americans want to build a transcontinental railroad? ?

Ineed a summary over thurgood marshall ! me

All of the following were weaknesses of the articles of confederation, except: a) the central government was not permitted to regulate state, interstate, or foreign trade. b) the central government was not permitted to borrow money. c) the central government had little ability to regulate money. d) the central government had no ability to tax.

What was the most explosive issue facing the united states prior to the start of the civil war?