How did the invention of the cotton gin in 1793 affect the use of slave labor in the South?

A rapid rise in the number of slaves in America.

Cotton production was very labor intensive. A bottle neck in the production was removing in seeds from the cotton. The cotton gin (short for engine) made this process much faster, making the cotton production much faster and more economical.

Much of the southern U.S. cotton made its way to textile mills in Britain. The increase in available raw cotton and the new industrialized cotton mills that could mass produce cotton fabric and a greater market for inexpensive cloth created a boom in cotton planting.

Cotton needs a lot of cheap labor to clear land, plant, harvest and refine cotton into bale form to be exported. Plantations used slaves for this purpose. The need for slaves grew in proportion. The anti-slavery movement grew also.

In the complex society of America the ingredients for the American Civil War were refined and grown.