You reminded me of the Lyndon B Johnson quote which seems more relevant that ever. "If you can convince the lowest white man he's better than the best colored man, he won't notice you're picking his pocket. Hell, give him somebody to look down on, and he'll empty his pockets for you."

The trouble with this quote is that it's too easy to misinterpret it exactly in favor of the people it's criticizing.

Racism is a system for pitting poor white people and poor black people against each other. But the perpetrators are not the people in the other tribe, they're the people telling you that there should be separate tribes.