The cotton gin energized cotton production and revitalized slavery because it made it possible to clean the seeds out of cotton easily and quickly. Up until that time, the kind of cotton grown on the mainland of the US was very difficult to separate from the seed. This meant that it could not be grown economically. The market for tobacco was drying up and slaves were becoming less useful. But then Whitney invented the cotton gin and it became possible to make a profit growing cotton. Cotton boomed in the South and so did the demand for slaves.