Coronavirus speeds world's retreat into national shells

It's not just goods and services that cross international borders every day — it's people, too. But now the world is retreating into national shells, and the U.S. is leading the way in discouraging international travel.

Driving the news: In recent days, the U.S. has banned foreigners from entering the U.S. if they have been in China within the past 2 weeks.

• It also imposed travel restrictions on citizens of Eritrea, Kyrgyzstan, Myanmar, Nigeria, Sudan and Tanzania — who between them have a population of more than 360 million.
• And it barred even U.S. citizens from enrolling in the Global Entry program that facilitates international travel, if they live in the state of New York.

Of note: This was roughly the same week that the U.K. left the EU, with seismic implications for the future of labor mobility both into and out of Great Britain.

How it works: If you've ever spent much time in a place with invisible international borders, you'll know how magical it feels. In places like Alsace, or the island of Ireland, hard borders mean war and bloodshed, while their absence means peace and prosperity.

How it fails: International trade is already suffering from the coronavirus, including the travel and tourism sector. In the present climate, it's harder than ever for companies and countries to reverse course and start rebuilding severed international links.

The big picture: Coronavirus may only be a short-term problem. Over the long term, however, the outlook is similarly bleak, thanks to the geopolitical consequences of global warming.

• A case can be made that the climate crisis caused Brexit. The British vote to leave the EU was in part a reaction to the sight of Germany accepting hundreds of thousands of refugees from the war in Syria. That war, in turn, was exacerbated, if not caused, by global warming.

The bottom line: When international travel and migration starts to decline, that's a bad sign for everybody except nationalists.

Go deeper: The global economic threat of the coronavirus