When terrorists strike, whether at a kosher supermarket in Paris or a black church in Charleston, it's natural to look beyond the specific circumstances of a specific murderer and ask about the broader cultural and ideological trends that lead to radicalization and legitimize violence. And in the case of Dylann Roof, we don't need to look far for at least one sign of this. A Confederate flag flies on the grounds of the South Carolina statehouse as a symbolic token of the state's official ideological solidarity with the cause of fighting and dying for the purpose of enslaving black people.

But the problem is much larger than a single flag in a single state — the United States as a whole is suffused with perverse symbolism that legitimizes anti-black violence.

Consider Forrest High School in Marshall County, Tennessee, named after Confederate General and Ku Klux Klan founder Nathan Bedford Forrest. Forrest also lends his name to a state park in Tennessee and the ROTC building at Middle Tennessee State University.

About a mile and a half from Charleston's Emanuel African Methodist Episcopal Church, where this week's shooting occurred, you'll find a public park featuring a monument "to the Confederate Defenders of Charleston" who broke the laws of the United States of America in a (thankfully) failed effort to keep the city's black population enslaved.

The church itself is located on Calhoun Street, named after former Senator, Vice President, Secretary of State, and Secretary of War John C. Calhoun, who, in his day, served as the leading theorist and politician of the white supremacist movement in American politics.

Calhoun died in 1850. When the country collapsed into civil war about a decade later, it fell to Jefferson Davis to take practical political leadership of the movement for violence and slavery.

Davis's project failed, but he is commemorated with a statue in the US Capitol Rotunda, a highway in Northern Virginia, and the names of counties in Louisiana, Texas, Mississippi, and Georgia. Militarily, the movement was led by Robert E. Lee, who is the namesake of more than a dozen public schools, among other things.

No doubt, the vast majority of people who support — or at least passively accept — this widespread commendation of the Confederate cause don't particularly mean anything by it. Certainly they don't intend to be sending the message to impressionable and perhaps somewhat disturbed young men that African Americans are less-than-equal members of the political community and that the use of illegal violence against their interests is justified.

But symbols — like words — carry meanings that stand independently of any individual person's subjective intentions. And in this case, the symbols' meaning is extremely clear — lawless violence in pursuit of white supremacy is not necessarily wrong and may at times be worthy of celebration.

It's a message that Dylann Roof may have heard all too clearly.