For slavery among Native Americans, see Slavery among Native Americans in the United States. For slavery in the colonial period, see Slavery in the colonial United States. For modern-day slavery, see Human trafficking in the United States.
Slavery in the United States was the legal institution of human chattel enslavement, primarily of Africans and African Americans, that existed in the United States of America in the 18th and 19th centuries after it gained independence and before the end of the American Civil War. Slavery had been practiced in British North America from early colonial days, and was legal in all Thirteen Colonies at the time of the Declaration of Independence in 1776.
By the time of the American Revolution (1775–1783), the status of slave had been institutionalized as a racial caste associated with African ancestry. When the United States Constitution was ratified (1789), a relatively small number of free people of color were among the voting citizens (male property owners). During and immediately following the Revolutionary War, abolitionist laws were passed in most Northern states and a movement developed to abolish slavery. Most of these states had a higher proportion of free labor than in the South and economies based on different industries. They abolished slavery by the end of the 18th century, some with gradual systems that kept adults as slaves for two decades. But the rapid expansion of the cotton industry in the Deep South after the invention of the cotton gin greatly increased demand for slave labor, and the Southern states continued as slave societies. Those states attempted to extend slavery into the new Western territories to keep their share of political power in the nation; Southern leaders also wanted to annex Cuba to be used as a slave territory. The United States became polarized over the issue of slavery, represented by the slave and free states divided by the Mason–Dixon line,