Middle-class advancement was once localized in the core of America's cities, but that is not so much the case today, as those areas are labeled a "barbell economy," divided between highly-paid professionals and low-skill service workers.

Brookings Institution notes as early as the 1970s, middle-class income in the inner cities started to shrink more than anywhere else. Today, in most US inner cities, the cores are more unequal than their surrounding suburbs, noted geographer Daniel Herz.

As the failed American inner city experiment nears the latter stages before a collapsing point, a new report from Time could be the final nail in the coffin for some American inner cities, as the article suggests "cities have already reached 'Peak Millennial' as young people begin to leave."