The legacy of slavery in America remains a divisive issue, with sharp political divides.

Some argue that slavery still contributes to modern economic inequalities. Others believe its effects have largely faded.

One way to measure the legacy of slavery is to determine whether the disproportionate riches of slaveholders have been passed down to their present-day descendants.

Connecting the wealth of a slaveholder in the 1860s to today’s economic conditions is not easy. Doing so requires unearthing data for a large number of people on slaveholder ancestry, current wealth and other factors such as age and education.

But in a new study, we tackled this challenge by focusing on one of the few groups of Americans for whom such information exists: members of Congress. We found that legislators who are descendants of slaveholders are significantly wealthier than members of Congress without slaveholder ancestry.

In 1860, one year before the Civil War, the market value of U.S. slaves was larger than that of all American railroads and factories.

At the time of emancipation in 1863, the estimated value of all enslaved people was roughly US$13 trillion in today’s dollars. The lower Mississippi Valley had more millionaires, all of them slaveholders, than anywhere else in the country.

Some post-Civil War historians have argued that emancipation permanently devastated slave-owning........

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