Isaac franklin spent part of Christmas Day 1833 assessing his company’s operations and making plans for the future. Writing from New Orleans to one of his business partners in Virginia, Franklin took a few moments out of his holiday to report that he had rented a new showroom in the city from which he would soon start making sales, and that sales up the Mississippi River at the company’s branch in Natchez, Mississippi, were going swimmingly.

Franklin had just come from Natchez, and he was happy to relay the news that he had seen “first rate prices and profits,” realized nearly $100,000, and likely outdone all of his competitors put together. He was also collecting outstanding debts from customers to whom he had extended credit, and he promised that he would soon send along some money, though he told his partner that he ought to consider rustling up additional funds from his banking connections if he could. Franklin wanted “four hundred more slaves this season,” and keeping the supply chain steady did not come cheap.

Franklin and his business partners, John Armfield and Rice Ballard, were the most important domestic slave traders in American history. Through their company, commonly known as Franklin and Armfield, they moved roughly 10,000 enslaved people out of Maryland and Virginia for sale in Mississippi and Louisiana. They transformed the domestic slave trade by demonstrating how white men could make it their profession, not just something they might do as a temporary means of earning extra cash. And they did it not only through remorseless violence but also by taking maximum advantage of the fact that enslaved people were considered both laborers and financial assets that could be integrated into the money markets and credit networks of early American capitalism.

In 1808, Congress banned the importation of enslaved people from overseas, but a domestic slave trade flourished in the United States during the first 60 years of the 19th century. From 1800 to 1860, more than 1 million enslaved people were forcibly moved across state lines, shifting American slavery’s center of gravity steadily southward and westward as slaveholders relentlessly pursued greater profits from cotton and sugar production.

Slave traders bore responsibility for executing the bulk of this massive forced migration, providing a labor force that made them indispensable to slavery’s expansion and thus to the broader economic development of the country. As conduits for the financialization of enslaved people and their movement across the country, men such as Franklin, Armfield, and Ballard facilitated the systematic extraction of capital from Black labor and Black bodies that circulated around the country and around the world, and that benefited nearly everyone but the enslaved themselves. Their business, which I explore in my forthcoming book, The Ledger and the Chain, utterly belies any notion that slavery sat at the margins of American society.

The domestic slave trade was no sideshow in our history, and slave traders were not bit players on the stage. On the contrary, the trade and its operators were pervasive in American life before the Civil War. They played vital roles in shaping the demographic, political, and economic contours of a growing nation, and we ought not fool ourselves into thinking we have left that past behind. In truth, we still live in the world that Franklin and Armfield’s profits helped build, and with the enduring inequalities that they and their industry entrenched.