A campaigner for 'Vote Leave' during a rally in Hyde Park in London. (Ben Stansall/AGENCE FRANCE-PRESSE via Getty Images)

Constanze Stelzenmüller is Robert Bosch senior fellow at the Brookings Institution.

For me as a German, the Brexit vote is the second great seismic shift of my lifetime. The first was the miraculous gift of the fall of the Berlin Wall in 1989, which led to a quarter-century of expanded freedom, prosperity, democracy and security in Europe. The question before us now is: Does Brexit mark the beginning of the end for this era of peace? Or can the European project be salvaged?

The key thing to understand now is that this referendum was not just about policy questions such as immigration, regulation or defense cooperation. There are sensible debates to be had about these issues; the United Kingdom and the European Union argued about them over four decades. David Cameron’s government successfully negotiated exceptions for the U.K. on almost all the topics it cared about. Today’s E.U. was shaped by British goals, such as enlargement, and Turkey’s candidacy. Tragically, all this made no difference to the “leavers,” and it did nothing for the “remain” camp.

The rest of the E.U. supported these concessions, because we were appalled at the prospect of the U.K. leaving Europe. We saw Britain as a force for reason and good — an ancient and resilient democracy, with a history of deep engagement with the continent and the world. It was a power to be reckoned with, even after it had lost its empire. It was a pillar of the West, a guardian of global order, with its supremely capable diplomats and armed forces, and an important voice for free trade and an active foreign and security policy in the E.U.

Postwar Germany sought atonement and reconciliation with Israel, with France and with Poland. But the countries we wanted to be like were the United States and Great Britain: open, liberal, outward-looking, defenders of civility and peace.

As for me, London was my diplomat father’s first posting, so I had the lucky fortune of an English childhood: roaming the history of the world in the British Museum on rainy Sundays, and endless summers in Cornwall, where nobody ever locked their doors, and the kindly grocer — to the delight of my mother — would not just deliver your shopping, but also put it on the kitchen table, or in the fridge if you were at the beach.

But this vote was not about policy, or concessions: It was about feelings, and fear. And in that sense, it has revealed Britons to themselves (and to us) in truly shocking ways.

Britain, it turns out, is bitterly and nearly equally divided into what Daniel Finkelstein of the Times has called Leavia and Remainia: Older citizens, workers and people living outside the large cities are terrified of what they see as a German-dominated European juggernaut, and voted Out. Urban dwellers, younger Britons and — it seems — all of Scotland voted In, and are now angry at what they see as an irresponsible and irreparable act of self-harm. Clearly, these divisions will endure. It is hard to imagine how the next government can heal them.

We other Europeans were dismayed to learn that the majority of our British neighbors (whom we thought we knew, and got along with) have harbored a toxic wellspring of animosity toward us. Be our guest and criticize the E.U., or German dominance; we worry about all that, too. But the memory of the lies and the dogwhistle allusions to Nazis will not soon recede.

For most of us in the Other 27, Britain has severed its ties with the E.U. for a delusion of sovereignty and control. For the average German — we share borders with 10 other countries, and our prosperity rests on world trade — this is just bizarre.

But we know that there are Leavian camps in all our countries. We have seen elsewhere (not least in the U.S. election campaign) how easy it is for the unthinkable to happen. And so we have to ask ourselves: Are the events of today in Britain a harbinger of what awaits us at home? The task for my generation now is to make sure that does not happen.