On March 14, 1794, Eli Whitney patented his invention, the cotton gin (“gin” being short for engine). The machine succeeded in making the growing of cotton profitable for farmers in the south by speeding up the separation of the cotton bolls (the fluffy part) from the seeds.
The unforeseen side effect of Whitney’s invention was that it made Southerners want to grow more cotton on larger plantations, and thus, bring more African slaves in to pick it. Between 1790 and 1808, when it became illegal to import African slaves, 80,000 slaves were brought to the American South.
Source: National Archives (archives.gov)