The Civil War is about to loom very large in the popular memory. We would do well to be candid about its causes and not allow the distortions of contemporary politics or long-standing myths to cloud our understanding of why the nation fell apart.

The coming year will mark the 150th anniversary of the onset of the conflict, which is usually dated to April 12, 1861, when Confederate batteries opened fire at 4:30 a.m. on federal troops occupying Fort Sumter. Union forces surrendered the next day, after 34 hours of shelling.

The Civil War has forever captured the American imagination (witness the popularity of re-enactments) for the gallantry and heroism of those who fought and died, but also for the sheer carnage and destruction it left in its wake. Anniversaries heighten that engagement, and I still recall the centennial of the war in 1961 as a time when kids with no previous interest in American history were exchanging Civil War trading cards along with baseball cards.

My neighborhood friend Jon Udis got a subscription to Civil War Times Illustrated, and our regular discussions of sports heroes Bill Russell, Johnny Unitas and Carl Yastrzemski were briefly interrupted by talk about Grant and Lee, Sherman and “Stonewall” Jackson.

But our conversations, like so many about the war, focused on people and battles, not on why the confrontation happened in the first place. There remains enormous denial over the fact that the central cause of the war was our national disagreement over race and slavery, not states’ rights or anything else.

When the war started, leaders of the Southern rebellion were entirely straightforward about this. On March 21, 1861, Alexander Stephens, the Confederacy’s vice president, gave what came to be known as the “Cornerstone speech” in which he declared that the “proper status of the Negro in our form of civilization” was “the immediate cause of the late rupture.”

Thomas Jefferson, Stephens said, had been wrong in believing “that the enslavement of the African was in violation of the laws of nature.”

“Our new government is founded upon exactly the opposite idea,” Stephens insisted. “Its foundations are laid, its cornerstone rests, upon the great truth that the Negro is not equal to the white man; that slavery subordination to the superior race is his natural and normal condition. This, our new government, is the first, in the history of the world, based upon this great physical, philosophical and moral truth.”

Our greatest contemporary historian of the Civil War, James McPherson, has noted that Confederate President Jefferson Davis, a major slaveholder, “justified secession in 1861 as an act of self-defense against the incoming Lincoln administration.” Abraham Lincoln’s policy of excluding slavery from the territories, Davis said, would make “property in slaves so insecure as to be comparatively worthless … thereby annihilating in effect property worth thousands of millions of dollars.”

South Carolina’s 1860 declaration on the cause of secession mentioned slavery, slaves or slaveholding 18 separate times. And as the historian Douglas Egerton points out in “Year of Meteors,” his superb recent book on how the 1860 election precipitated the Civil War, the South split the Democratic Party and later the country not in the name of states’ rights but because it sought federal government guarantees that slavery would prevail in new states. “Slaveholders,” Egerton notes, “routinely shifted their ideological ground in the name of protecting unfree labor.”

After the war, in one of the great efforts of spin control in our history, both Davis and Stephens, despite their own words, insisted that the war was not about slavery after all, but about state sovereignty. By then, of course, slavery was “a dead and discredited institution,” McPherson wrote, and “(to) concede that the Confederacy had broken up the United States and launched a war that killed 620,000 Americans in a vain attempt to keep 4 million people in slavery would not confer honor on their lost cause.”

Why does getting the story right matter? As Mississippi Gov. Haley Barbour’s recent difficulty with the history of the civil rights years demonstrates, there is to this day too much evasion of how integral race, racism and racial conflict are to our national story. We can take pride in our struggles to overcome the legacies of slavery and segregation. But we should not sanitize how contested and bloody the road to justice has been. We will dishonor the Civil War if we refuse to face up to the reason it was fought.

E.J. Dionne’s e-mail address is ejdionne(at)washpost.com.