I believe the answer is: the Columbian Exchange
Columbian exchange refers to the exchange of knowledge, labour culture, plants , and animals that heppened between countries in american continent during the 1500s. When the exchange happens, different races crossbreed with one another which resulted in the birth of new races.
Answer:
C - the expansion of slavery in the South
Explanation:
With the invention of the cotton gin, more workers (slaves) were needed to work the fields to increase the amount made from the cash crop.