> What if it actually came to that? If push came to shove and the interior decided to push a nativist, nationalist agenda, what if the coastal regions that benefit significantly from trade were to say "Okay, you guys can play with yourself, we're going to play with the rest of the world."

I think if it actually came to that, it would eventually mean war. The interior economy falls apart, coastal regions secede, the poor countries would inevitably be driven to war against the coastal regions out of desperation. Extreme nationalism would just make this more likely. No one should think this is a good idea.

Also, saying coasts are "well-integrated into the world economy", implying the rest of the country is not, is just a horribly myopic view of the world. They are only "well-integrated" because the government chose and planned that explicitly - globalization and free trade as an economic policy, removal of protectionism (e.g. NAFTA, etc) and heavy subsidies of the industries involved (especially tech, via military spending).

It didn't have to be that way - it isn't because tech, finance, whatever is more meritocratic or anything. With more sensible protectionism you could have international trade while still preserving your country's manufacturing base, allowing the rest of the country's economy to also be "well-integrated". But labor is expensive in developed countries, corporations want more profit, and our government doesn't particularly prioritize the working class.