German police check vehicles at the border crossing between Salzburg in Austria and Freilassing in Germany | EPA Forum The end of Schengen How a human tsunami has shattered a European dream.

LONDON — No country is more committed to European integration than Germany. All the grand schemes to bring Europeans together — the single currency, the push for common policies, the abolition of frontier controls within the European Union — have Germany at their heart.

But Berlin’s announcement Sunday that it is to reimpose frontier controls with Austria strikes a deadly blow at of one of the few agreements that has turned these visions into reality — the Schengen treaty, which removed passport controls along thousands of miles of Europe’s frontiers.

Is Schengen now dead? And is this the beginning of the end for an “ever closer union” in Europe?

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Germany insists that its new border check points are temporary, an emergency response to the thousands of migrants pouring in from the south. When the human tsunami dies down, the interior minister suggested, these controls will be lifted, the trains from Austria will start running again and Germany will continue to champion a Europe without borders.

It sounds like wishful thinking.

For more than a year, Europe has been struggling with an ever-increasing flow of desperate migrants — refugees from wars and persecution in Syria, Iraq, Libya and Afghanistan, young men fleeing dictatorship in Eritrea, poor people from across Africa and the Middle East seeking a better life. They have been smuggled across the Mediterranean in leaky boats, transported like cattle in airless lorries, forced by gangs to clamber across frontiers in Turkey, Greece and the Balkans. And almost all have had one destination: Germany.

Altogether, estimates say, some 800,000 may arrive in Germany in one year. And Germany, like Sweden, the only other European nation to have offered shelter to so many, now finds that its voters have had enough. Unless the flow is cut back or stopped, there will be riots, violence and racial attacks. Angela Merkel’s government is reeling and populists are denouncing cherished European principles.

This is not the first time a country has temporarily reimposed border controls, permitted under the 1985 Schengen treaty (now incorporated in EU law) in cases of emergency or national security. But the move comes as the clamor for a permanent crack-down becomes ever louder, not only in Germany but also in France, Italy, Hungary and the European heartlands.

It is not only the refugee crisis that has exposed the failings of a frontier-free Europe: the exploitation by organized crime of the open borders to escape into other countries, safe in the knowledge that there will be no hot pursuit and little police intelligence to catch them, has caused rising anger and frustration.

Free movement around 26 countries for 400 million Europeans is now seriously threatened.

And then there is terrorism. The recent attempted murders by a gunman on a train from Amsterdam to Paris highlighted the ease with which terrorists can travel across borders to plot massacres. Interior and transport ministers warned after an emergency meeting in Paris there would have to be more spot checks, proper cross-frontier intelligence and amendments to Schengen to impose controls when necessary.

This triple assault means that free movement around 26 countries for 400 million Europeans is now seriously threatened. Many Europeans look enviously at Britain and Ireland, which were granted opt-outs when the treaty was signed, and still retain full border inspections — with some notable success in stopping terrorists and catching illegal immigrants. No such option is open to anyone else. The 1997 Amsterdam treaty insisted that any new EU applicant had to remove internal frontiers. Three non-EU members, Switzerland, Iceland and Norway, have already joined in. Three new members, Romania, Bulgaria and Cyprus, will be forced to do so soon.

European idealists and those desperate to keep frontiers passport-free argue that new border checks would not solve any problems. The challenges are mostly from outside Europe. The refugees will keep coming, they say, and human traffickers will still evade border police. Terrorism knows no frontiers. And organized crime often has its roots far beyond Europe. They argue that political crises in the Middle East — war, extremism and religious persecution — must still be resolved, and border controls treat the symptoms rather than the causes.

These are poor arguments. Schengen, the treaty bearing the name of the little Luxembourg town where it was signed, has two massive weaknesses that have never been properly tackled. First, it will only work if Europe’s common external frontier is massively strengthened. But where is this frontier? Often in countries least able to cope, running between Greece and Turkey, Malta and Libya, Hungary and Serbia, Sicily (Italy) and Tunisia. Only a paltry sum has been given to Frontex, the EU border force, to boost patrols, stop drug smugglers and check migrants. Secondly, the intelligence formerly gathered at frontier posts is never now properly passed on. Countries have no way of tracking who is entering or leaving unless police data is routinely made available.

The real weakness of Schengen, however, is that it runs counter to the growing mood in Europe.

This is more nationalist, more insular, suspicious of Brussels, skeptical of pan-European solutions, resentful of paying out for poorer neighbors, determined to reassert more local control and angry at the remoteness of decision-making. It is not a pretty or an idealistic mood. It has been fanned by the repeated crises over the euro, a growing north-south divide, austerity, slow economic growth and Europe’s utter failure to find common solutions to the tragedies of migration and asylum.

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While Brussels dithers, populist parties demand quick national solutions. Little wonder that Marine Le Pen is said to be on course to win power in France or that smaller countries accuse Germany of imposing austerity on all of them. Schengen is in danger of being the first victim of this mood, as governments scramble to show voters that they are in command.

A blanket re-imposition of border posts would be hugely expensive, cause massive delays and anger tourists and businessmen alike. But not everyone needs to be stopped. Passport controls could be selective, based on intelligence or random inspections. The mere possibility of interrogation would strengthen security across Europe. It works in Britain and Ireland. Germany may find that having imposed checks with Austria, it will now have to do the same on every frontier if human trafficking is to be halted.

And despite the wailings of European idealists, the general public would not object. Schengen’s days are numbered.

Michael Binyon is a foreign affairs analyst and former diplomatic editor of the Times of London.