One hundred and fifty years ago today, America ratified the 13th Amendment, abolishing slavery throughout the country. It was a momentous victory. But it also prompted a protracted campaign to whitewash how slavery would be remembered, one waged in Southern parks and squares, on the region’s university campuses and statehouse grounds. By the 1930s, Confederate monuments stood watch all over the South, buttressing a white supremacist interpretation of the past.

Finally this year, after the Confederate sympathizer Dylann Roof murdered nine black worshipers in Charleston, S.C., protesters began to demand the removal of proslavery memorials and flags from the commemorative landscape. This movement has now spread beyond the South and beyond the issue of slavery, as students from Bowdoin, Princeton and other schools have pushed their institutions to rethink the honors they have bestowed upon prominent racists.

The desire to purge these tributes is understandable. But in a country that teaches its history through monuments, it is not enough to tear down troubling and inaccurate memorials, a solution that has costs as well as benefits. What the United States needs is a national memorial that tells the truth about slavery and its victims.

White Americans have long used monuments to propagate a flawed understanding of slavery and its role in the Civil War. When Charlestonians raised a memorial to the South Carolina statesman John C. Calhoun in 1896, they praised his dedication to truth, justice and the Constitution — ignoring his devotion to slavery, which he famously called “a positive good.”

Hundreds of similar monuments convinced generations of white Southerners, and others, that the Confederacy had gone to war to defend states’ rights, liberty and the Southern way of life. Anything but slavery. ...