During the 18th century, the demand for slaves increased as the cotton economy expanded.
- Slavery was abolished in the northern states by the 1800s, and there were few slaves in the West.
In 1860, however, there were nearly four million slaves in the South.
By 1860, the enslaved population of the United States had reached nearly four million people, and slavery was legal in all but five states and the District of Columbia. The vast majority of slaves were held in the South, where the plantation economy was heavily dependent on slave labor. In the years leading up to the Civil War, the issue of slavery became increasingly divisive, and the disagreement over the expansion of slavery into new territories was a major cause of the war.