How was the U.S. Civil War a significant factor in that country’s future as a world power?

a.) The Civil War increased the geographical size of the United States, and thus its world influence.
b.) The war gave the United States a lead in advanced armaments, which solidified its power.
c.) With slavery ended, the United States could at last join the community of civilized nations.
d.) By keeping the nation united and large, the war ensured the future strength of the United States.