He had to be carefully taught

A young man wears Rhodesian and apartheid-era flags on his jacket. Neither country existed during his lifetime. Both flags are commonly worn as in-group insignia among politically organized white supremacists. He poses with a gun and a Confederate battle flag, time-honored banner of the Ku Klux Klan and other Southern hate groups. He takes photographs of himself at the Museum and Library of Confederate History and at the slave quarters of a historic plantation. "You have to be carefully taught," as the old song from "South Pacific" puts it. He slaughtered nine African Americans in a church.

Dylann Roof told his victims that he came "to shoot black people" because they are "raping our women and taking over our country." The latter claims date back to the white supremacy campaigns of the 1890s, one of which overthrew the government of North Carolina, by the way. These ideas did not just percolate up inside of his mind; this is not ordinary "bias" or suspicion of people different from him; someone had to teach him these elaborated historical traditions. (Watered down versions of them are ordinary enough in mainstream Southern politics.)

He gunned down nine people at a historic black church, historic enough that he might well have selected it intentionally; Emanuel AME has been at the center of the civil rights struggle since the early 19th century. The Denmark Vesey slave rebellion of 1822 was organized out of this church, which white mobs burned in retaliation in addition to executing many church members. The slave revolt that it was designed to launch was planned to occur on June 16 — the anniversary of Dylann Roof's massacre; of course, there is no evidence that he knew this history, but no evidence that he didn't, either.

Roof said he wanted to start a race war; this is a common theme among politically organized white supremacists and depicted in their favorite book, "The Turner Diaries," which also helped inspire Timothy McVeigh to commit the Oklahoma City bombings. He is part of something, and something dangerous. America in general and South Carolina in particular are generously sprinkled with white supremacist groups.

Shelby, where he was caught, has long been a Klan hotbed. Some years ago, the White Patriot Party committed a mass murder some years back of several men they believed to be gay; the leader who ordered that murder committed mass murder at a synagogue in Kansas City only a few years ago. The road Dylann Roof was captured on, Dixon Boulevard, was named after Thomas Dixon, perhaps the most illustrious white supremacist in the history of the world, apart from Hitler. Dixon wrote 28 white supremacist books one of which, "The Clansman," provided the basis for "Birth of a Nation," America's first film blockbuster that glorifies the Reconstruction-era KKK and was shown at the White House in 1915. There is no evidence that Roof knew this, of course, nor that he didn't, though he was clearly obsessed with history. Roof's probable mental frailty most likely made him susceptible to such influences. It's almost certainly both/and with respect to mental illness and white supremacy, but there is at least as much evidence for the latter as for the former.

(Timothy B. Tyson is education chair of the North Carolina NAACP and a senior research scholar at Duke University.)