The Robert E. Lee statue in Charlottesville, a rallying site for white nationalists, is a monument to the country’s moral confusion about the Civil War. (Evelyn Hockstein/For The Post)

“There was a right side and a wrong side in the late war which no sentiment ought to cause us to forget.” So proclaimed the famed abolitionist Frederick Douglass in 1878, fighting back against an ascendant movement among whites for “reconciliation” — a movement premised on the idea that Americans should honor both the Union and Confederate veterans of the Civil War for their martial valor. Douglass knew that such a movement drew a false moral equivalency between the Union cause and the Confederate one — and he knew the danger such a false equivalency represented for him and other African Americans.

Donald Trump has fulfilled Frederick Douglass’s prophecy. In his statements since the violent white supremacist riot in Charlottesville, Trump has attempted to draw a parallel between neo-Nazi rioters, the Ku Klux Klan and anti-Semites on the one hand and counterprotesters on the other. Trump’s false equivalency draws from a long history. It is rooted, in part, in our culture’s persistent moral confusion about the Civil War, the product of 150 years of active manipulation of the origin, meaning and outcome of the war.

The seeds of that confusion were sown in the war’s closing hours by Robert E. Lee and his fellow leaders of the Confederacy. In his iconic “Farewell Address” to his defeated army at Appomattox, Va., in April 1865, Lee attributed the Union’s victory to its “overwhelming numbers and resources.” The Union victory was, in his view, a show of brute force, not of courage and skill, and a triumph of might over right. This view became, in the ensuing decades, a central tenet of the “Lost Cause” ideology that glorified slavery, the Old South and the Confederacy. White Southerners were willing to “reconcile” with the North at the end of Reconstruction only if they could lay claim to their own piece of the moral high ground.

From the very start, leaders such as Abraham Lincoln, Ulysses S. Grant and Douglass rejected the “might over right” interpretation. In their view, the Union victory was the triumph of right over wrong, attributable to the courage, skill and righteousness of the Union army and the moral and material power of free society. For Union soldiers and their commanders, liberation meant the deliverance of the white Southern masses from the domination of slaveholding oligarchs.

Over the course of the war, most loyal Americans came to see the emancipation of slaves and the enlistment of black troops as essential to Union victory. By the war’s end, the Union army reflected America’s diversity. More than 25 percent of Union soldiers were immigrants. Two hundred thousand African Americans, the majority of them formerly enslaved Southerners, fought for the Union. Three hundred thousand white men from slave states wore the Union blue; while most of them came from the four slaveholding border states that rejected secession, 100,000 of these white Unionists came from Confederate states. Many of these Union soldiers hoped that their patriotic sacrifices would earn them full acceptance and integration into an American society that had oppressed or marginalized them.

Union soldiers and the civilians who supported the war effort as nurses, spies, scouts and so on were not, by modern standards, all moral paragons. They were 19th-century people living in a culture that was saturated, in the North and the South, with racism and social hierarchies, and they were divided among themselves over how much social change the war should bring. But the fact remains: There was a profound and fundamental idealism at the heart of the Union war. The Union represented for loyal Americans the triumph of democracy over oligarchy, of unity over division, of freedom over tyranny, of truth over falsehood.

During the postwar Reconstruction, former Confederates launched a propaganda campaign designed to preempt and turn back social change. That campaign disparaged Union soldiers as “mongrels” and “mercenaries”; cast race relations as a zero-sum-game in which any advances for blacks would spell the degradation of whites; and conjured the violence the Klan and other white supremacist terrorists used to drive the Unionist coalition out of Southern politics.

Former Confederates systematically sowed chaos and then blamed it on the agents of change, claiming that the violence would end only when the old order was restored. These tactics stoked the fears and prejudices of Northern and Southern whites alike, and set the stage for a reconciliation movement among them that memorialized the martial prowess of white Civil War soldiers — Union and Confederate — and obscured the history of emancipation and black military service.

The Lee statue in Charlottesville, erected in 1924 at the behest of an arch segregationist, represents a long-standing project of white supremacists: to distort the history of the Civil War by casting the Confederacy as morally blameless and the Union’s victory as fundamentally illegitimate. The statue is, among other things, a monument to a false equivalency — to the idea that Confederates are equally deserving of a place of honor in modern America as Union soldiers.

To remove the statue is not to erase history, as so many have claimed. It is vitally important to preserve the artifacts and documents of Confederate history in the places — libraries, museums, national battlefield parks — designed for such purposes. But Charlottesville’s Lee statue, looming large over a public square in a modern, diverse city, is itself an erasure of history. It seeks to deny the true nature of the Civil War: a triumph of right over wrong, not might over right. It is past time to remove it, not as an act of erasing history, but of setting the historical record straight.