Much of what we think we know about the domestic slave trade and domestic traders of enslaved people in the United States is wrong. To the extent most Americans think about the slave trade at all, they usually envision traders as people so brutal that no decent person would associate with them. Many imagine the trade itself as an element of slavery so hideous that even enslavers shied away from it.

From the unctuous trader Mr Haley in Harriet Beecher Stowe's 1852 novel Uncle Tom's Cabin, to the enslaving Brodess family in the 2019 film Harriet whose threats to sell Harriet Tubman signify the family's malevolence, traders of enslaved people and the slave trade have long served as shorthand for the evils of American slavery at its extremes.

But the historical facts tell a different story. Buying and selling enslaved people was no aberration in the United States before the Civil War. On the contrary, the domestic slave trade was ubiquitous in the slave states. It was an engine of national economic growth. And Americans often viewed it as a reasonable way for White men to make their fortunes. We will never reckon effectively with the institution of slavery and its legacies so long as we shy away from these uncomfortable truths about the slave trade and the traders of enslaved people who made it profitable.

In 1808, Congress banned the importation of enslaved people from Africa and the Caribbean. But the ban resulted from economic and political considerations as much as moral ones, and no comparable legislation restricted commerce in enslaved people within the boundaries of the United States. Indeed, through the importation ban the Federal Government created a protected domestic market in human beings, and it did so precisely at a moment when demand for enslaved labour from cotton and sugar planters in Alabama, Mississippi, Louisiana and other lower South states was escalating dramatically. Hundreds of men, in turn, saw opportunities to profit by filling that demand as traders of enslaved people.

In the first 60 years of the 19th century, roughly one million enslaved people were forcibly migrated across various state lines, more than twice as many as had been taken into the Transatlantic Slave Trade to mainland North America in two centuries. At least two million more enslaved people were bought and sold within individual states.

To be sure, the domestic slave trade was hideous. It systematically wrenched apart enslaved families, and its victims were often subjected to journeys of a thousand miles that ended in some of the harshest labour environments on the planet.

Nevertheless, the trade took place openly on city streets and country roads, in taverns and hotels, on the steps of courthouses and in private offices and public auction houses. Dozens or hundreds of people being marched across North America for sale were common sights for travellers, as was the spectacle of enslaved people being loaded and unloaded from coastal slave ships that plied the ports of the Atlantic and the Gulf of Mexico. The trade entailed the complicity, and often the active engagement, of bankers, merchants, bureaucrats, law enforcement officers and politicians. And it generated massive amounts of capital that flowed throughout the nation.

Traders of enslaved people, meanwhile, were undeniably brutal people who inflicted remorseless violence and unfathomable cruelty in the regular course of their business. But they were not necessarily the social outcasts that enslavers and other defenders of slavery routinely insisted they were. Many were instead regarded as trustworthy businessmen and respected members of American society. In fact, the more successful a trader was, the more likely that was true.

Consider, for example, the lives and careers of Isaac Franklin, John Armfield and Rice Ballard, who were the most powerful and influential domestic traders of enslaved people in American history.

In 1828, Franklin and Armfield went into business together, creating a company known as Franklin and Armfield that dealt in enslaved people. Armfield made purchases in Maryland and Virginia, using an Alexandria townhouse with an attached walled compound as his offices and holding pen. He then sent the enslaved people, mostly by ship, to New Orleans, where Franklin received them, sold some of them in the city and brought the rest up the Mississippi River to Natchez for sale there. A few years later, Franklin and Armfield brought Ballard on as a third partner and stationed him in Richmond, where he expanded the company's geographic reach.

By the middle of the 1830s, Franklin and Armfield was the largest slave-trading operation in the United States. The company ran advertisements every day in multiple newspapers, announcing that it would "pay Cash for any number of LIKELY NEGROES". It had a network of agents stationed in cities and towns throughout the Chesapeake who scoured tens of thousands of square miles for enslaved people to purchase. It owned three of its own ships on which Armfield sent scores of enslaved people to the lower South as often as every two weeks, and he frequently arranged for company vessels to bring back cotton, sugar and other commodities for delivery to northern merchants. The company had established credit relationships with leading banks from New York to New Orleans, and it helped to circulate tens of thousands of dollars at a time from the Second Bank of the United States, which held the money of the Federal Government.

Franklin and Armfield ceased active trading in enslaved people in 1836, by which point the company had trafficked nearly 10,000 enslaved people. But the three partners continued collecting debts from customers for years, and they emerged from the trade as some of the richest men in the country, with wealth that measured by inflation alone would be the modern equivalent of tens of millions of dollars.

While Franklin and Armfield attracted the ire of antislavery activists, the company remained in good standing among planters, merchants and bankers, all of whom gave it their business because of the partners' reputation for straight dealing. Leading politicians from both of America's leading political parties vouched for Franklin's character, with Andrew Jackson calling him "an honest and high-minded man". Henry Clay called him "a gentleman of honour", and when Franklin died in 1846, newspapers in every state in the country reported the news.

Ballard became director of a Natchez bank and a prominent cotton planter with land and slaveholdings in multiple states, and upon his death he was described by a newspaper in Louisville, where he sometimes lived with his family, as “an old citizen, much esteemed, and beloved by all who knew him”. Armfield, meanwhile, bought a resort hotel in the Tennessee mountains, where he hosted economic, political and religious elites from across the South every summer for years. When Armfield died in 1871, newspapers praised him as “a friend to virtue, an advocate of morality, and a supporter of Christianity”.

The notion that traders of enslaved people were ever wholly reviled pariahs emerged even as men such as Franklin, Armfield and Ballard demonstrated its falsehood. Crafted by many of the same White southerners who did business with traders as a matter of course, it was a self-serving myth that let enslavers displace their own responsibility for sustaining the trade and the inhumanity it entailed. The myth survived emancipation, became part of larger mythologies that aimed to defend slavery and the Confederacy even after they were no more and took hold in the nation as a whole. But it was no less self-serving, as it concealed how integral slavery and the slave trade had been to American prosperity.

The connections between race and economic inequality in the United States have an extensive and often disturbing history. But if we are to see and do battle with those connections in our own time, we have to look unflinchingly at how they came to be. The history of the domestic slave trade and domestic traders of enslaved people, after all, shows us that the consequences of deciding not to look too closely can be devastating, and they can last for centuries.

• Joshua D. Rothman is professor of history and chairman of the department of history at the University of Alabama. He is the author of three books including, most recently, The Ledger and the Chain: How Domestic Slave Traders Shaped America