Update (0200ET) : Leaders of the 26 European countries that are part of what is normally a free-movement zone also agreed Tuesday to shut their external borders to most nonresidents for the first time.

"We are faced with a serious crisis, an exceptional one in terms of magnitude and nature," European Council President Charles Michel said late Tuesday. "We want to push back this threat. We want to slow down the spread of this virus."

Other leaders phrased it in martial terms: "We are at war," French President Emmanuel Macron said Monday.

Until last week, citizens of the E.U. could move across the continent with ease, even as the virus slowly spread across its population. Just as a resident of Maryland can easily pack bags and head to Virginia, so, too, could a Pole cross into Germany.

But no more.

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As The Gatestone Institute's Soeren Kern detailed earlier, as a growing number of countries close their borders to fight the coronavirus pandemic, the European system of open internal borders - a cornerstone of European integration - is on the brink of collapse.

The so-called Schengen Area, which comprises 26 European countries, entered into effect in 1995 and abolishes the need for passports and other types of control at mutual borders. It is a key practical and symbolic achievement of European integration and is now falling apart.

In a move packed with political significance, Germany, the largest and most powerful country in the European Union, on March 16 introduced controls on its borders with Austria, Denmark, France, Luxembourg and Switzerland after it registered 1,000 new cases of Coronavirus Disease 2019 (COVID-19) in just one day.

Anyone without a valid reason to travel, German Interior Minister Horst Seehofer said, would be turned away at the borders. Travelers with symptoms of COVID-19 would be refused entry as well. German citizens and anyone with a residence permit, however, will be allowed to reenter Germany.

"Protecting our population also requires measures to reduce the risk of infection from global travel," Seehofer said. "We are dealing with a very aggressive and fast-spreading virus. We will have to deal with it for months. As long as there is no European solution, you have to act in the interest of your own people."

The decision to impose border controls represents a major reversal by the German government. Just a few days earlier, on March 11, German Chancellor Angela Merkel said, "In Germany, we believe that border closings are not the answer to fight the spread of the Covid-19 epidemic." Her sentiment was echoed later that day by German Health Minister Jens Spahn, who stated, "We are not going to get rid of the virus by closing our borders. The virus is already with us and we have to get used to the idea."

On March 15, the German newspaper Bild reported that Merkel was still blocking all attempts by members of her cabinet to impose border controls. The infighting, however, had cost Germany valuable time in trying to contain the spread of the virus.

Writing for the influential German blog Tichys Einblick, commentator Ferdinand Knauss, explained that Merkel was blocking border controls because the dogma of open borders is an ideological pillar of Merkelism:

"In the face of the corona crisis, there were apparently discussions in the Federal Government about what most of our neighboring countries had long since done: consistent protective measures at the borders. Several of our neighboring countries — Denmark, Poland, Czech Republic, Austria — have largely closed their borders. In most countries, people from at-risk areas are strictly controlled upon entry. Not in Germany. You do not have to guess very long who prevents this. Only the Chancellor can do that. But why is she doing it? "In that fateful year of 2015, the 'open borders' became a conditio sine qua non [indispensable condition] for the continuation of Merkelism. That is why the dogma must be maintained. Merkel knows that the instruction to close the border, in general to take consistent national measures to protect her own citizens, would be tantamount to her own declaration of political bankruptcy. "So, as citizens become aware of the threat and their demand for protection increases, the corona crisis also becomes a crisis of Merkelism. It already is, as Merkel's rejection of border protection measures shows. One of the decisive questions will be how the media, which are still largely loyal to Merkel, and the political and social establishment weigh in: The morality of openness to the world versus the protection from threats. The greater and more painful the risk of corona, the harder it will be to neglect the need for protection. "Merkel is now fighting. But as always in her chancellorship, she is not fighting for her country and its citizens, for which she is responsible. She is fighting for her power, for her legacy. When the citizens come to understand this, the corona crisis will have been Merkel's last fight in the political arena."

Merkel's stance had left Germany increasingly isolated, as a growing number of Schengen countries have introduced border controls:

Austria . On March 10, Chancellor Sebastian Kurz announced controls along the border with Italy and a ban on the entry of most travelers from there. Kurz said, "The utmost priority is to prevent the spread and thus the importing of the illness into our society. There is therefore a ban on entry for people from Italy into Austria, with the exception of people who have a doctor's note certifying that they are healthy." Interior Minister Karl Nehammer also announced a ban on all air or rail travel to Italy.

Slovenia . On March 11, Health Minister Ales Sabeder stated that the government had closed some border crossings with Italy and started making health checks at those remaining open in order to combat the spread of the coronavirus. He said that citizens would only be able to cross the border in six places while all other roads that crossed the border would be closed. Normally more than 20 crossings are open. Passenger train transport between the two countries has also been stopped and most bus companies have canceled routes to Italy. Sabeder said that foreigners with Slovenian residence permits would be allowed to enter Slovenia if they had a certificate that they have tested negative for coronavirus during the previous three days.

Poland . On March 13, Prime Minister Mateusz Morawiecki announced that, as of March 15, only Polish citizens or people with a Polish residence permit would be allowed to enter the country. Everyone returning home from abroad would be quarantined for 14 days. All international inbound passenger flights or trains are banned, but freight transport is not affected. "The state will not abandon its citizens," Morawiecki said. "In the current situation, however, we cannot allow ourselves to keep borders open to foreigners."

Switzerland . On March 13, the Swiss government reimposed border controls with other European countries. Switzerland, although not a member of the European Union, is part of the Schengen zone. Justice Minister Karin Keller-Sutter said that travel restrictions from Italy were aimed at preventing Italian patients from seeking access to Swiss hospitals. Asylum seekers were also subject to the restrictions. Swiss citizens, holders of a resident permit as well as cross-border workers and people transiting through Switzerland are still allowed to enter the country.

Denmark . On March 14, Prime Minister Mette Frederiksen imposed border controls on all traffic by air, land and sea until at least April 13. Danish citizens are allowed to enter but any non-Dane without a valid reason for travel will be denied entry. "We stand on uncharted territory," Frederiksen said. "We are in a situation that looks nothing like what any of us have experienced before. It is going to cost us all. If we do not do this, we risk that the costs, human, health and financial, will be far, far greater."

Hungary . On March 16, Prime Minister Viktor Orbán announced that, effective immediately, all passenger traffic into Hungary would be halted and only Hungarian citizens allowed to enter the country. Previously, the government had imposed controls on the country's borders with Austria and Slovenia. All train travel was halted between Hungary and Croatia, Slovenia and Ukraine.

Spain. On March 16, Interior Minister Fernando Grande-Marlaska decreed the reestablishment of controls at all land borders. Only Spanish citizens, people with Spanish residency and cross-border workers will be allowed to enter national territory by land. The measure does not affect the transport of goods.

The Czech Republic, Estonia, Greece, Latvia, Lithuania and Slovakia, in a bid to combat the spread of the coronavirus, also imposed border controls. Other European countries that are not part of the Schengen system, including Albania, Bulgaria, Romania, Serbia and the Republic of North Macedonia also introduced border controls.

The Bulgarian Foreign Ministry, which advised its citizens to avoid travelling abroad, described the current state of affairs:

"The situation at the land borders of European countries is constantly and drastically changing, which makes it impossible to travel to or from Bulgaria with all modes of transport. "With regard to the prevention of the spread of the coronavirus, there is almost no country in Europe that has not at the moment introduced restrictive measures — border closures or separate border crossing points, enhanced border controls, shutdown of flights, closure of airports."

The break-down of Europe's system of open borders has been met with anger by those in favor of European integration. During a March 13 press conference in Brussels, Ursula von der Leyen, head of the European Commission, the administrative arm of the European Union, warned member states not unilaterally to close their borders:

"The Single Market has to function. It is not good when Member States take unilateral action. Because it always causes a domino effect. And that prevents the urgently needed equipment from reaching patients, from reaching hospitals and the medical personnel. Ultimately, it amounts to reintroducing internal borders at a time when solidarity between Member States is needed."

In a desperate effort to save the Schengen system, Von der Leyen on March 16 proposed a 30-day entry ban into the European Union. The idea apparently was that if the EU's borders were closed to the outside world, individual member states would not have to close theirs.

Ironically, just a few days earlier, Von der Leyen had condemned the March 11 decision by U.S. President Donald J. Trump to impose a 30-day ban on continental Europeans traveling to the United States. "The European Union failed to take the same precautions and restrict travel from China and other hotspots," Trump said. "As a result, a large number of new clusters in the United States were seeded by travelers from Europe."

On March 12, Von der Leyen issued an angry statement:

"The Coronavirus is a global crisis, not limited to any continent and it requires cooperation rather than unilateral action. "The European Union disapproves of the fact that the U.S. decision to impose a travel ban was taken unilaterally and without consultation."

Von der Leyen now says that she will present the EU heads of state with a proposal to ban "unnecessary trips" to the Union. The entry ban would initially be for 30 days but could be extended if necessary. "The fewer trips there are, the more we can contain the virus," she said.

Anja Krüger, the pro-EU business editor for the German newspaper Tagesspiegel, noted:

"It is breathtaking how the borders in Europe are closed in the wake of the corona crisis, how one country after another seals itself off. The pandemic shows how fragile the European Union is.... "After the pandemic subsides, will everything be the same as before, as if nothing had happened? The question is how far the corona crisis is capable of an ad hoc destruction of a slowly growing European awareness among the people in the EU member countries over the years. "Much will depend on how the crisis is managed. However, the fact that the return to nationalism was carried out quickly and firmly will arouse desires among opponents of European unification. What goes once, goes again and again."

In a March 13 press conference, the president of Italy's hard-hit Veneto region, Luca Zaia, said that Europe's borderless zone was "disappearing as we speak." He noted that the stringent border controls imposed by Austria shows that Schengen "no longer exists and will be remembered in the history books."