Eli Whitney, a young New Englander, invented a cotton gin in 1793 which automatically cleaned cotton. This transformed the southern economy, making cotton "king" and greatly increasing the need for slaves.

After the Revolutionary War, the Southern United States sought a new cash crop to replace indigo, the trade for which had shifted to India during the conflict. Cotton emerged as a potential candidate, but traditional long-staple cotton (also known as Egyptian cotton) could only be grown on the Atlantic coastal islands of the U.S., as it required a very long growing season and sandy soil. The alternative was short-staple cotton, which could thrive in the Southern interior. However, this variety of cotton had sticky seeds that were extremely difficult to separate from the lint, making processing labor-intensive and inefficient. This is where Eli Whitney came into the picture.

Eli Whitney was born in Westborough, Massachusetts, in 1765. He was the son of a small farmer who also ran a small manufacturing business on the side. As a boy, Whitney made nails for ships, demonstrating an early knack for mechanical work. After studying at Yale, he moved to South Carolina to work as a tutor. There, he learned about the challenges of cleaning (or “ginning”) cotton and began to think of a mechanical solution.

Whitney designed a machine that used a roller studded with half-inch-apart nails. When turned, the nails on the roller passed through a grid, pulling the cotton lint through the grid while leaving the seeds behind. The lint was then separated from the nails, and the seeds fell off separately. Whitney’s invention allowed a single worker to gin as much cotton in one day as previously required 25 workers, making upland cotton economically viable for the first time. Whitney patented his cotton gin, but because it was relatively simple, many people copied it. Whitney tried to enforce his patent rights, but this proved challenging. In the end, most of Whitney’s income from the cotton gin came not from manufacturing it in a Connecticut factory he established, but from compensation provided by state governments. South Carolina paid him $50,000 for patent infringement, North Carolina compensated him with $30,000 through a special cotton tax, and Tennessee contributed $10,000.

The impact of the cotton gin was unprecedented. In 1793, the United States produced about five million pounds of cotton, nearly all of which was the Sea Island variety. This output represented less than 1% of the world’s cotton production. By 1860, however, the U.S. was producing two billion pounds of cotton, accounting for over 75% of global production.

The growth of cotton production had a profound effect on slavery. Before the cotton gin, the demand for slaves was relatively low, and enslaved individuals were not considered particularly valuable; a slave could be bought for around $300. By the time of the Civil War, however, the price of a slave had soared to $3,000. Cotton farming was highly labor-intensive, and despite the efficiencies introduced by the cotton gin, the expansion of cotton agriculture greatly increased the demand for slave labor. In this way, Whitney’s invention, while advancing agricultural productivity, also contributed to the entrenchment of slavery in the Southern economy.