The British referendum to leave the European Union is a massive shock to the European political order. But what are its implications for U.S. foreign policy?

Conventional wisdom dictates that a vote for Brexit was the undesirable outcome for the United States. That is probably right: any economic instability is undesirable at a time of slow growth and fragile confidence.

That said, the danger that Brexit poses to U.S. foreign-policy interests, at least in the short term, can be overstated. The United States’ principal long-term interest in European integration is that it prevents major interstate war on the European continent. Britain did not join what was then the European Economic Union until 1973. Historically, Britain has been an outside intervener, rather than a protagonist, in European wars. France and Germany are the vital EU members; as long as they remain, the European Union will continue to fulfill its raison d’être of preventing war among the great powers of Europe.

And this is where Brexit looms most ominously: the biggest danger is that the British vote will embolden Marine Le Pen and anti-EU activists in other core EU countries to depart the EU. Indeed, this is already happening. A French exit would end the European project and revive geopolitical competition in Western Europe. That would be a major setback for U.S. foreign policy; in the twentieth century, great-power conflict in Western Europe drew the United States into two bloody wars.

The broader lesson of the Brexit vote is similar to  Donald Trump's success in the Republican presidential primary. The narrative arc is that many citizens of advanced industrialized countries have lost faith in governing elites and institutions. Indeed, that loss of faith is so deep that these voters are willing to upend institutions that have presided over an era of unprecedented material prosperity.

Part of this can be attributed to deindustrialization, globalization and mass immigration, which have so dramatically reshaped life in many Western countries over the past forty years. To be sure, many of the resulting changes have been for the better. Yet the benefits have been unevenly distributed, with some feeling left behind or even betrayed.

The vital question now facing the European Union is what can be done to repair that loss of trust before it inflicts far greater damage. Most Europeans agree with the core elements of the original European Economic Community: free movement of goods and people among countries with comparable wealth, living standards and cultures. At the same time, many dislike centralized European decisionmaking on monetary and fiscal policy, criminal justice, welfare, refugees and large-scale economic migration from poor countries.

Europe would be wise to ensure that countries that want the former but oppose the latter are not forced into a binary in-or-out choice, as Britain was. This may be a bitter pill for those Europeans devoted to the dream of “ever-closer union.”  But the more important dream is that which motivated the visionaries who conceived the European Coal and Steel Community, the EU’s progenitor, in 1950: peace in Europe. Brexit warns that it may not be possible to have both.

Adam Klein is a Visiting Fellow at the Center for a New American Security, a Council on Foreign Relations International Affairs Fellow and a former Robert Bosch Foundation Fellow in Berlin.

Image: Nikos Koutoulas/Flickr