Edward Baptist, author of The Half Cannot Be Told: Slavery and the Making of American Capitalism (2014):

“Southerners created numerous financial innovations that were essential to the process of the domestic slave trade. Slave owners put mortgages on slaves as they bought them. Britain had abolished slavery, but you can essentially buy slaves by buying one of those bonds….The idea that the commodification and suffering and forced labor of African-Americans is what made the United States powerful and rich is not an idea that people necessarily are happy to hear. Yet it is the truth.”

Stretching out beyond the slave South, the story encompassed not only Washington politicians and voters across the United States but also Connecticut factories, London banks, opium addicts in China, and consumers in East Africa. The Bank of the United States (in which federal funds were deposited) was lending money to slave traders. Planters would mortgage their slaves to raise money, and those mortgages were sold to investors. Huge increases in cotton-picking over the course of the antebellum period were due almost entirely to violence against slaves. Historians have often attributed that increase to the emergence of new, easier-to-pick strains of cotton and the cotton gin.

In 1860 a typical slave picked at least three times as much cotton a day as in 1800. The crop of cotton in 1859 was astonishing—almost 2 billion pounds of clean fiber in 4 million bales. Slavery’s productivity was higher than ever—some 700 pounds per enslaved man, woman, and child in the cotton country, twenty-two times the rate in 1790. In the 1850s cotton production in the southern states doubled to 4m bales and satisfied two-thirds of world consumption. By 1860 the four wealthiest states in the United States, ranked in terms of wealth per white person, were all southern: South Carolina, Mississippi, Louisiana and Georgia.

In 1860, the Southern slave labor camps provided 88 percent of the cotton used in Great Britain's cotton mills. Cotton had become the number one trading commodity of the entire world. It fueled the industrial revolution, feeding not just the cotton mills of Britain, but also the ones in towns like Lowell, Massachusetts. The cotton mills of Lowell were built with the profits made from the unpaid labor of African Americans in the slave labor camps. Cotton went from 14 percent of total American exports in 1802 to 61 percent by 1860. The United States share of the worldwide cotton market climbed from one percent in 1801 to 66 percent by 1860.

As new lands were opened by the Louisiana Purchase and the forced eviction of almost 50,000 Native Americans from the lands to which they held title, slavery moved from the coastal states of the Old South to the new Southwest. Foreclosed from importing new slaves to work the new land by the Act Prohibiting Importation of Slaves of 1807, slave traders forced the migration of one million slaves.

From the 1790s to the 1860s, enslavers moved 1 million people from the old slave states to the new.