Why did the institution of slavery expand from 1775 to 1830?
There were two main reasons for the expansion of slavery—the cotton gin's invention in 1796 and the United States' westward expansion. The cotton gin allowed one slave to do the work of many since it removed seeds from cotton quicker than by hand. This allowed cotton planters to plant more cotton, thus making a lucrative crop in the United States even more profitable.
Before the Civil War, the South had more millionaires than any other region in the United States. These millionaires were able to turn their profits into buying more acreage and more slaves, thus keeping themselves at the top of the economic chain and leaving the poor behind in a highly stratified system.
Cotton is a very harsh crop on the soil and cotton planters were always in search of cheap land. This is the main reason why Southerners went to settle in East Texas and why Andrew Jackson coveted the southeastern United States for his southern constituency. As more acres were planted, the cotton kingdom grew and thus the demand for slaves with it. This created tension between Southern slaveowners and Northern abolitionists.
Another factor that should be considered is that the North increased its number of textile mills, but this would be more prevalent after 1830, and there was already a strong demand for Southern cotton in Europe in the time period between 1775 and 1830. The growing demand in cotton fueled the demand for the slaves to work the large plantations.
The single most important reason for the barbaric growth of slavery in the United States was the invention and subsequent patent of Eli Whitney's Cotton Gin. By the 1830's there was a popular saying among the souths largest plantation owners; 'the cotton gin made slavery pay'. The United States Constitution prohibits any further importation of slaves in 1808, however with the invention of the cotton gin, the patent, and those interested in benefiting from its financial potential, the value of slavery rose rapidly. In addition, although the importation of slavery was prohibited after 1808, the number of slaves in America grew every year. Any child born of a slave was the property of the slave owner, therefore it was not uncommon for slave women to basically be kept pregnant as often as possible. (forced) The cotton gin was responsible for doubling the amount of cotton produced every ten years post 1800. Combine this profit incentive in conjunction with all the other new industrial inventions of the time, such as the new and improved textile machinery of northern businesses along with the surplus of cheap industrial immigrant labor available in the northern cities and the growth of slavery was liken to collateral damage.
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The institution of slavery expanded during this time period largely due to the opening up of new land where slavery could exist and due to the invention of the cotton gin.
During this time period, America expanded inland to some extent. Slaves moved into new areas like Alabama and Lousiana and Mississippi as these areas became part of the United States.
Perhaps more important, though, was the development of the cotton gin. Before this machine was invented, slavery was dying out as the tobacco industry became less viable. After the cotton gin was invented, cotton became a much more profitable crop. As cotton production increased, the need for slaves increased as well.