Before the cotton gin was invented, it was difficult to make a profit from cotton. The only cotton that was grown in the South was the "green seed", which was a short-staple type of cotton. Unfortunately, this type of cotton was very labor intensive and time consuming. It took hours to remove the seed from the fibers.
Before the cotton gin, the South's economy consisted of cash crops such as rice and tobacco. Slaves were used in plantations to help harvest these crops, but overall, slavery was declining since owning a slave was expensive. Many plantation farm owners couldn't afford slaves. Since slaves were becoming less profitable, slavery was thought to be abolished. After the cotton gin was invented, slavery drastically increased.