[Sun Belt]

How is this different from every single other city in the history of planet Earth? It's not.

1] The City becomes crowded and expensive.
2] Residents of that city want/need more space to accommodate their household and also want it to be less expensive [they have to plan for college, cars, weddings etc]
3] The urban footprint moves outward to accommodate the economic conditions that persist in the city in able to pay for city services and to accommodate additional people wishing to live in that area.

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What happens when China loses 3-4 hundred million people this century? Yikes. This is a new frontier.