A facinating look at how global economics works.
One theory for why rich cities tend to get richer is "cumulative advantage," which is more commonly known as the rich-get-richer principle. The idea is that cities with thriving industries (consulting in Boston; software in San Jose; commodities in Chicago) attract the smartest workers, whose talents add to the success of those industries, redoubling their ability to attract the smartest workers. Talent attracts talent. Business attracts business. A growing tax base supports better schools, nicer parks, and safer neighborhoods. Economic growth thrives on a feedback loop that, from a certain angle, appears to be infinite and unbreakable. In short: The rich get richer, forever.
And sometimes they do. It is hard to imagine a future for the Bay Area or New York City that looks like Flint, Michigan. The catch, however, is that 35 years ago, the city with the highest median wage for workers under 35 was, in fact, Flint, Michigan.
Nothing lasts forever. The only jobs that aren't portable are digging ditches in your town or selling burgers on your corner. Even those are subject to shifts in the global economy.