These days almost everyone has the (justified) sense that America is coming apart at the seams. But this isn’t a new story, or just about politics. Things have been falling apart on multiple fronts since the 1970s: Political polarization has marched side by side with economic polarization, as income inequality has soared.

And both political and economic polarization have a strong geographic dimension. On the economic side, some parts of America, mainly big coastal cities, have been getting much richer, but other parts have been left behind. On the political side, the thriving regions by and large voted for Hillary Clinton, while the lagging regions voted for Donald Trump.

I’m not saying that everything is great in coastal cities: Many people remain economically stranded even within metropolitan areas that look successful in the aggregate. And soaring housing costs, thanks in large part to Nimbyism, are a real and growing problem. Still, regional economic divergence is real and correlates closely, though not perfectly, with political divergence.

But what’s behind this divergence? What’s the matter with Trumpland?

Regional disparities aren’t a new phenomenon in America. Indeed, before World War II the world’s richest, most productive nation was also a nation with millions of dirt-poor farmers, many of whom didn’t even have electricity or indoor plumbing. But until the 1970s those disparities were rapidly narrowing.