Why did the cotton gin encourage more slave labor?

The cotton gin encourage more slave labor because the cotton gin needed handwork to work the machine.

A group of slave would pick out the cotton and hand it over to the other slave and the salve would work the machine with the cotton gin to remove the cotton fibers from the seeds. Then further on, it would be process into shirts, pants, dresses, and all other sorts of goods.

Hope this helps! :) -from peachimin