<em>Slave labor.</em>
Explanation:
Slavery was immensely popular in the Southern states, as they focused on agriculture and cultivating cash crops. Cash crops were crops that sold for a lot of money, particularly overseas. These crops included tobacco, indigo, and cotton. Since the Southern states relied on agriculture for their wealth, they relied on labor in order to maintain these plantations.
At first, the South would rely on indentured servants. These were people who got their passage bought from Europe and in order to repay their buyer, would work for them for a number of years. This eventually was deemed to be too much to work, as this only lasted for a number of years, so the South turned to slavery quickly.
Since the Northern colonies focused on industrialization, they did not use slave labor and were often against the concept of it. This eventually caused the Civil War, as the North and South disagreed on if slavery was moral or not.
