In America, we make much of our multiculturalism, as if to say that while the rest of the world may still be subject to ugly blood feuds, our exceptionalism will keep us safe. Tribalism is something that other, lesser peoples do. But in fact, our overtly tribalistic past is relatively recent. As a boy growing up in 1960s Maryland, racial and ethnic slurs that today would be considered appalling were an important part of our lingua franca, and we used them freely among ourselves. During a college break, I recall hitchhiking down Interstate 95 into the South and being greeted by an immense billboard picturing a sword-wielding hooded knight on a charger with the message "The Ku Klux Klan welcomes you to North Carolina." Later, when my African-born wife and I walked the streets of our Baltimore neighborhood we sometimes became the target of insults from black men practicing their own sad brand of racism.