What major industries emerged in the decades after the civil war?

Consider the following invention from the american industrial era. cotton gin – a machine that removed seeds from short-staple cotton which option explains how this invention contributed to the role of the united states as an emerging world power? a. it was in high demand abroad, as many european nations had begun farming cotton. b. it led to the decline of slavery in the south, which enhanced america’s international reputation. c. it freed up many slaves to become factory workers in northern cities, which improved the economy. d. it increased production efficiency of a us cash crop that was in high demand in other nations.