During the civil war, the south’s use of enslaved labor gave it
a. an almost unlimited supply of soldiers.
b. more workers for its factories.
c. a way to keep plantations running.
d. a way to disrupt northern industry.

The answer to your question would be C. a way to keep plantations running.

i also think it is c

roosevelt believed that in light of the country's recent military successes, it was unnecessary to use force to achieve foreign policy goals, so long as the military could threaten force. this belief, and his strategy of “speaking softly and carrying a big stick,” shaped much of roosevelt's foreign policy.