Eli Whitney patented his cotton engine, or “gin,” in 1794. A mechanical device to separate cotton fibers from cotton seed, it dramatically lowered the cost of producing cotton fiber. Formerly, workers (usually slaves) had separated the seeds from the lint by hand, painstaking work that required hours of work to produce a pound of lint. By mechanizing the process, the gin could produce more than 50 pounds of lint per day. Cotton fabric, formerly quite expensive due to the high cost of production, became dramatically cheaper, and cotton clothing became commonplace. In the early decades of the 19th century, Southern farmers shifted more and more of their acreage into highly profitable cotton production, and large-scale plantation agriculture became common in the Deep South states of Georgia, Mississippi, Alabama, and Louisiana.
The gin's effect on the economy and on the lives of the slaves who made up a significant part of that economy was complex. The cotton gin freed slaves from the arthritic labor of separating seeds from the lint by hand. At the same time, the dramatically lowered cost of producing cotton fiber, the corresponding increase in the amount of cotton fabric demanded by textile mills, and the increasing prevalence of large-scale plantation agriculture resulted in a dramatic increase in the demand for more slaves to work those plantations. Overall, the slave population in the South grew from 700,000 before Whitney's patent to more than three million in 1850—striking evidence of the changing Southern economy and its growing dependence on the slave system to keep the economy running.