I know I responded to you once already, but the other thing I wonder is if globalization is really the issue here. There's also an inherent productivity gap between densely and sparsely populated areas. Had industrial jobs not moved to China, they would have moved to the cities.
When people do build factories, which they still do, they build them in or around the cities, not in the country, despite having to pay more for land, labor, and regulatory compliance. If they do locate in the country, they choose a town that has a university and a hospital.
That's not really as true any more. The plastics and chemicals industry is growing rapidly in Ohio and Pennsylvania, and those factories tend to be sited based on easy access to natural gas supplies rather than proximity to cities.
When people do build factories, which they still do, they build them in or around the cities, not in the country, despite having to pay more for land, labor, and regulatory compliance. If they do locate in the country, they choose a town that has a university and a hospital.