The correct answer is "The internal slave trade within the US grew dramatically."
There were multiple reasons as to why the internal slave trade grew. One of them was the fact that the Atlantic slave trade, where US citizens got many of their slaves, was abolished as of 1808. Along with this, the cotton gin made it easier to pick seeds out of cotton. This ease in production caused a skyrocket in profits for those plantations that could produce mass amounts of cotton. This results in southern plantation owners trying to trade for as many slaves as possible, so they could continue to make significant profits.
