The first key factor in creating the domestic slave trade was an insatiable demand for labor from expanding plantation regions in the South. The second essential element was the availability of a ready supply of enslaved people - a supply made possible because North American slave numbers, unlike those in the rest of the Americas, grew by natural increase (that is, numbers of births exceeded numbers of deaths). By the 1730s, the enslaved populations of Maryland, Delaware, and Virginia were rapidly growing. A decade or so later, even those of colonies south of Virginia began to experience continuous and rapid natural increase. In the latter colonies, though, the expansion of the plantation regime was so great that the importation of enslaved men, women, and children was seen as essential.

In the 1760s, Pennsylvania, New York, New Jersey, and Massachusetts were exporting some of their bondspeople to the Southern colonies. This trend is verified for example by evidence in the South Carolina Gazette, where advertisements referred to numerous men and women who had been brought from these Northern colonies. In the 1770s, slave traders, also called speculators, regularly advertised in the Boston Gazette for "healthy slaves, . . . Male or Female who have been some years in the Country, of twenty Years of Age or under." As slavery declined in the mid-Atlantic and northern states, owners began to sell their slaves to traders who moved them further south.  The scale of the trade from the North is suggested by alarm in South Carolina that northern blacks might undermine the discipline of the local enslaved population. In 1792, for example, citizens of Beaufort, South Carolina, petitioned the state legislature complaining about the "notorious" practice of Northerners, who "have for a number of years past been in the habit of shipping to these Southern states, slaves who are scandalously infamous and incorrigible."    

     The export trade from Delaware, Maryland, and Virginia was very well established by the 1780s. At the Constitutional Convention of 1787, Charles C. Pinckney explained that Virginia "will gain by stopping importation [from Africa]. Her slaves will rise in value and she has more than she wants."  South Carolina and Georgia whites called out for slaves - and newspaper advertisements of 1787 show that Virginia was ready to supply them. The trader Austin Moses advertised in Richmond, Virginia, for: "One hundred Negroes from 20 to 30 years old for which a good price will be given. They are to be sent out of state, therefore we shall not be particular respecting character of any of them - hearty and well made is all that is necessary."

Moses was one of many who regularly sent enslaved Virginians to the expanding plantation regions further south and west.

The interregional movement of the enslaved population was made up of two elements. The substantial majority - from 60 to 70 percent (or 1.2 million people) - migrated by the long-distance domestic slave trade, while the rest were part of planter migrations. In the latter case, planters looking for new opportunities moved all or most of their slaves together to work new western land.

Slavery and the Internal Slave Trade in the United States of North America by Theodore Dwight Weld

By the 1790s, Maryland, Delaware, and Virginia had become the main exporting areas, the bulk of their "shipments" going to Georgia, Tennessee, Kentucky, the Carolinas, and the sugar-planting regions of Louisiana. But by the 1820s the Carolinas and Kentucky were exporting more people than they were importing.

Joseph Dickinson Papers

Thirty years later, Tennessee, Missouri, Georgia and Alabama had joined the ranks of net exporters. From 1760 until the Civil War, the number of men, women, and children traded to the South and West increased substantially during each decade, with the exception of the 1840s when numbers slackened.

	Progression Of The Slave Population In Selected Southern States (table)
	Statistical view of the United States, embracing its territory, population - white, free colored, and slave - moral and ...

Some historians have argued that selling south occurred because land in the exporting states was exhausted. According to this argument, "soil exhaustion" meant that agriculture was in decline in the exporting states, and those states could not support a growing slave population. This traditional argument seems to misrepresent the true situation, however. In fact, farming still flourished in the exporting states, but selling people offered the chance of further profit. For example, in South Carolina during the 1850s, 65,000 African Americans were transported out of state, but still the state’s cotton production rose by 50,000 bales and its enslaved population increased by seventeen thousand.

Tyre Glen Papers

The trade was motivated purely by profit, and enslaved men, women, and children went to markets that offered the highest profits. Some were sold at major urban marketplaces such as New Orleans and Natchez, but most were dispatched directly to scattered rural communities.

The Domestic Slave Trade in Mississippi and the Forks of the Road Slave Market at Natchez by H. Clark Burkett and Jim Barnett

In 1846, speculator T. W. Burton wrote from Lowndes County, Alabama, "There is a vast quantity of negroes in the Market here" and traders were offering slaves in every village in the county. The area, he said, was "full of negroes." Moving on to Mississippi, Burton found that "there is negroes [offered by traders] all through the state." Most traders covered several counties in seeking out buyers.  A fellow speculator reported that Dr. Thomas C. Weatherly, a typical trader, "Lives in his tents. He told me he sold ten negroes last week at fair prices. [As a means of meeting customers] he is following the counties round attending the courts."