Answer: B. Production of cotton
Explanation: The invention of the cotton gin in this 1793 tied the economy of the Southern states to cotton production. By the 1860, production of cotton by the South represented more than half of all American exports. This led to the rapid expansion southwest as Southerners needed more land to cultivate cotton, as it had proved to be the crop of choice.
This allowed the American South to expand its wealth and population and became an integral part of an increasingly global economy. Also, because of its trading and export potentials, merchants from the Northeast, Europe, Canada, Mexico, and the Caribbean flocked to Southern cities, setting up trading firms, warehouses, ports, and markets.
