Messages of solidarity with France are flooding in from across the continent. But beneath the talk of unity and common anxiety, three dividing lines are opening up across Europe. How they are resolved will determine whether the European Union emerges stronger with its values intact — or if its fragile unity is blown apart by the terrorists.

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First is the divide between those who want to close national borders and those who want to develop a common European response.

News is still emerging and contradictory, but it suggests the attacks have pan-European roots: a French national who had been monitored by anti-terrorist services, accomplices from Belgium possibly supplied with arms by a Montenegrin; the finding of a likely forged passport of a Syrian who entered Europe via the Greek island of Leros before making his way westwards through the Balkans.

Hours after the attack, the new Polish government linked Paris to the EU’s refugee policy — and threatened to walk away from its quota. The Slovak prime minister, Robert Fico, did the same. Even before the Paris attacks, European Council President Donald Tusk warned that “saving Schengen is a race against time.”

Austria, Germany, Slovenia, Hungary, and Sweden have all taken moves to reinforce their borders. Paris brings to the fore with renewed urgency questions about the restraint over known terrorist suspects, and of police and intelligence co-operation and border controls.

Just as important are the political manifestations.

In France, the question currently is whether this will help the National Front. But across the whole Europe, we are seeing the emergence of parties that appeal to what political scientists call “threatened majorities” — majorities whose fear of demographic change makes them behave like minorities.

Renaud Camus — an intellectual associated with the far right in France — laid out this regressive philosophy in a book, ‘Le Grand Remplacement,’ which argued that within one to two generations, France’s European population will be replaced by visible minorities as a result of immigration and differential birth-rates.

He sees a triple movement where the European population is de-spiritualized and deprived of its cultural identity by transnational ideologies such as globalizing capitalism, anti-globalization leftism, and Islamism. This kind of thinking — driving the advances of the right-wing PEGIDA and Alternative für Deutschland in Germany, the Danish Peoples’ Party, the Sweden Democrats and UKIP — also has a big impact on mainstream parties and consequently on the options for a common European response.

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The second dividing line is around the idea of a war on terror.

France’s President François Hollande and Prime Minister Manuel Valls are using martial language and calling ISIL a terrorist "army." But many Europeans have spent 15 years criticizing the U.S. for launching a Global War on terror after 9/11 (not least for providing the Russians and others with the opportunity to accuse the West of double standards).

If the Paris attacks were directly orchestrated by ISIL from Syria/Iraq, the language of war would be more appropriate than in the case of al Qaeda, given that ISIL is a proto-state. But if there will be a big military engagement of France plus three or four partners against ISIL as coalition in a 'war on terror', how will other member states, not part of the coalition, relate to this?

After 9/11, the U.S. conducted a global military campaign that seemed to overturn accepted rules of international law on targeting, detention, interrogation and so on. Will France fight in a way that respects the international rule of law (including making reasonable arguments in areas where the law is unclear) or further undermine its global reach?

Lost in the attention to Paris is the fact that the U.S. this weekend conducted its first anti-ISIL strike outside Iraq/Syria, killing the leader of ISIL in Libya. Should Europeans start to follow suit? And what about captured ISIL fighters, whether European nationals or not, whether in Syria/Iraq or in Europe? Do they all go before a court? Could they be held in detention without trial as prisoners of war? It is not hard to imagine divisions between EU member states over these difficult questions.

What air strikes against ISIL can achieve is another question. Very little, if they are not part of a wider political strategy that will include work with troops on the ground and a broad participation of the regional actors. A U.N. resolution that will get Russia, Iran, Saudi Arabia, Qatar and Turkey on board would be the first step, if difficult, in such a strategy. In any case, defeating ISIL in Iraq and Syria is one thing; preventing it from leading or inspiring attacks in Europe is another. The language of war must not let us lose sight of the fact that Europe needs much more than just a conventional military response.

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That raises a third question, another line of possible division: what the confluence of the terrorist and the refugee crises will do to Europe’s relations with its neighbors.

We are seeing the rise of the security paradigm in Europe’s foreign relations as we move from a period where Europeans felt they were shaping the world to one where they feel that it is shaping us. One of us wrote a book in 2005 arguing that Europe would run the 21st century — developing a type of transformative power that could help change former communist dictatorships into market democracies by implementing 80,000 pages of European laws, or inspire change to our neighbors in the Rose and Orange revolutions.

But today the boot is on the other foot. The Middle East is exporting chaos rather than importing democracy. Africa and the western Balkans are working out how to leverage their new-found power.

For EU unity, the big question is how we deal with our biggest and most divisive neighbors. Russia hopes that our desperation about refugees and fear of terrorists will give it great leverage over us. In Turkey, Recep Tayyip Erdoğan realizes that he won’t face lectures about his authoritarian tendencies so long as he can threaten to open his borders.

At the Vienna talks on Syria, there were apparently some real breakthroughs: agreement on what a political roadmap could be; the promise of internationally supervised elections in exchange for acceptance from the West that Bashar al-Assad can stand, and corresponding pressure on both sides for ceasefire. But the Geneva talks on Syria in the past showed that no road map will work unless there is a perception of seriousness among the regional actors who are to enforce it. It will be for Europe to define clearly its line of action, and get the international actors on board.

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Although it was Paris that was attacked, it is not just the French president who is exposed by these three divisions. Germany’s Angela Merkel also finds herself in the front line. She has been the glue that held Europe’s responses together on the euro, on Russia, on Brexit. She has been fighting an increasingly lonely battle within the European Union to reconcile the continent’s moral and legal obligations on refugees with hardening public opinion. Now her critics are using Paris as further proof of her perceived lack of control (“Kontrollverlust”) over the refugee crisis.

We have seen Merkel weakened at home by in-fighting among her Christian Democrats and on the European stage by member states refusing to comply with their quotas. But if she is defeated, it is not just Europe’s response to the terror or refugee crisis that is at stake — we risk a wider disintegration on Russia, the euro and even the British question. All member states are affected by the region sinking into chaos. We must hope that Paris brings Europeans back together again — underpinning the language of solidarity with common action and a refoundation of the European project around shared values.

Mark Leonard is Director of the European Council on Foreign Relations. Vessela Tcherneva is its Director of Programmes.