Photo by Carnotzet from the Torontoist Flickr Pool. North American cities are undergoing a massive change. And it's not just gentrification, Alan Ehrenhalt writes in The New Republic, it's a wholesale "demographic inversion." In Chicago, Atlanta, Washington, and elsewhere, the poor, minorities, and immigrants are being pushed to the outskirts while the affluent—and, in this context, overwhelmingly white—professional class colonizes the downtown core. The trend reverses the massive migration of the affluent out to......