content: They were first ghettos for ethnic Europeans, who made something of themselves and moved out or up ...leaving the void that called for the "need" for slaves from the south to come up....they've been building up businesses and moving up and out creating a void for Hispanics...who are building up restaurants and moving up and out.  The common theme is that once you "make it" you get the fuck out of the hellhole areas where more of "your people"  get left behind than what stick around. There's always more groups around the world to bring in for that next group to take the place of the current demographic .