What does a city do when the primary economic driver disappears? Social unrest and economic often are symptoms, rather than causes of urban failure.
Since 1950, the rankings of US Cities, except #1 NYC, have fundamentally reordered even as the population doubled from 150 to 330 million people (and as many as 20 million non-citizens-legal or otherwise). Suburbanization has a key factor here, but the key is the de-industrialization of the Rust Belt cities. Was it de-industrialization, crime, racial tensions, freeways or something else? What does this say about NYC?
