Since after World War II, nearly every major American cities experienced white flight, which left major urban areas with predominantly black population.
For the past few decades, however, a stark (yet quiet) reversal is taking place: "a demographic inversion" that is re-shaping the make up of American cities.
In this interesting piece for The New Republic, Alan Ehrenhalt discussed the "reverse white flight" phenomenon, its causes and how it would affect urban life:
In the past three decades, Chicago has undergone changes that are routinely described as gentrification, but are in fact more complicated and more profound than the process that term suggests. A better description would be "demographic inversion." Chicago is gradually coming to resemble a traditional European city--Vienna or Paris in the nineteenth century, or, for that matter, Paris today. The poor and the newcomers are living on the outskirts. The people who live near the center--some of them black or Hispanic but most of them white--are those who can afford to do so.
Link - Thanks Eric Zimmermann!
It's money... not necessarily race.
It's the only way to be sure.
Suburbia is more for families. When you're married and have kids and such, you don't have as much time or desire for the interaction of urban life and things like cultural events and restaurants and clubs and such aren't as convenient or affordable or desireable. Suburbia is dull and lonely for singles and childless couples.