What started as a distant civil war in Syria, with rebel factions challenging the authoritarian government of President Bashar Assad, has become Europe's war, with no easy end in sight.

Although Assad still clings to power, four-and-a-half years of conflict have turned Syria into a failed state, providing a haven for Islamic State militants who are a key cause for the exodus of migrants to Europe, and have used Syria as a base for plotting bloody assaults on Europe as well.

The coordinated attacks in Paris brought suicide bombing to France for the first time and left 129 dead, driving home the dangers of having an extremist group in control of territory so close to Europe. The attacks come as Europe is divided and vulnerable to social and economic shocks.

Anand Menon, professor of European Politics at King's College London, said the Islamic State group is attacking at a time when EU unity is already badly frayed by a prolonged financial crisis, Russia's intervention in Ukraine, and Britain's attempt to redefine its relationship with the EU ahead of a referendum on whether to abandon the bloc. Europeans are also increasingly at odds over whether to welcome or reject the refugees in their midst.

"Islamic State is pushing at an open door," said Menon. "If their intention is to divide Europeans, this is happening already. You take what they said: That this attack is retribution for French intervention in Syria. This infects the British debate about getting involved in Syria, and will make the Germans more allergic to using force. Europe is very fragile right now."

He said the financial crisis is opening a "north-south" divide, with Italy and Greece feeling the pain of EU-imposed austerity cuts in public spending, even as they cope with ever larger refugee numbers.

There is no European consensus on whether to use more force against Islamic State strongholds, and no consensus on how to cope with the arrival of so many people seeking a better life in Europe.

As some European leaders use air strikes to try to weaken IS in its self-declared Caliphate in parts of Syria and Iraq, the radicals' siren call has seduced some European Muslims, triggering a small but steady flow to Syria, with some returning home with murderous intentions.

Full details of the planning are not yet established, but the slaughter of civilians on a balmy November night made clear the radicals' intention to bleed Europe as well as Syria and Iraq.

At least one of the attackers appears to have blended into the flow of hundreds of thousands of refugees seeking safety in Europe. A Syrian passport found at one of the sites had been traced back through the refugee trail from Macedonia to Greece.

The Islamic State extremists have relied on modern methods to penetrate European society. They use social media acumen to lure new recruits from Europe, a passage eased by jet travel that can bring newcomers to the continent within hours, and IS used their social networks to claim responsibility for the orchestrated Paris killings.

At the same time, the flow of refugees from war in Syria and elsewhere has exposed a fundamental weakness in the 28-nation European Union, making it abundantly clear that Europe's rattled leaders do not agree on how to cope.

The concepts of open borders and the free movement of people, foundation stones of the EU integration project, are being challenged as never before.

Time and again, at emergency summits, the EU has announced solutions to the refugee situation with little subsequent impact on the deteriorating conditions on the ground.

More than 700,000 people have arrived in the EU so far this year, and EU officials have been unable to process them in an orderly way despite announced relocation plans and quota systems.

Eastern European countries have been reluctant to implement EU mandates requiring them to accept more refugees — with Hungary's parliament rejecting the plan and Slovakia planning to challenge them in court — and the divisions are expected to deepen now that there is a tentative link between the Paris attack and the refugee flow.

Poland's incoming minister for European affairs, Konrad Szymanski, said that in light of the Paris attacks, Poland cannot implement an EU agreement to accept 7,000 refugees — and must implement stricter border controls with security concerns paramount.

The unresolved battle for supremacy in Syria has also has spiked tensions with Russia, which backs the Assad government and has used its bombs to attack not just Islamic State strongholds, but also those of some more moderate rebel factions backed by Europe and the United States.

Russia, too, has paid in blood for its Syria policy. The IS extremists blamed Russia's bombing campaign for its apparent downing of the Metrojet airliner over Egypt that killed 224 people last month.

In Europe, the attacks, coupled with the migrant crisis, are sure to fuel the "keep them all out" view embraced by far-right leaders. The migrants can expect to feel this backlash as they arrive in Europe with high hopes and few possessions, and Europe's millions of law-abiding Muslims worry about an increase in the suspicions directed their way.

Any stiffening of anti-immigrant and anti-Muslim sentiment suits the militants in Syria. Analysts say they want more, not less, political polarization in Europe.

The Islamic State group expresses a deeply felt hatred of what it calls "infidels" and opposes European beliefs in personal liberties, freedom of expression, and the separation of church and state. In a statement claiming responsibility for the coordinated attacks, IS called Paris "the capital of prostitution and obscenity." IS believes in the glory of religious-based martyrdom — in fighting to death at home and now on European soil.

The impact of Syria's meltdown goes far beyond the borders of France. It includes the huge economic cost of housing and resettling so many displaced people all at once.

It's been felt in Britain, where Syria-based extremists have proved adept as using social media to lure young men and women into their ranks. British officials are seeking new powers in Parliament to expand surveillance operations to "detect and disrupt" what is said to be an unprecedented number of plots. They are specifically targeting Internet communications favored by IS recruiters.

Prime Minister David Cameron said Monday seven planned attacks have been thwarted in the last six months and that the government is aware of Syria-related cells operating inside Britain.

It's been felt in Germany, which has seen more than 750,000 migrants flood across its borders this year. Chancellor Angela Merkel has stuck with her catchphrase "we will manage it," but her optimism is finding less and less support within her own conservative bloc — especially in Bavaria, the entry point of almost all of the newcomers.

And while it is in Paris that the Syria fallout is most acute right now, all of Europe finds itself reeling from a harsh wake-up call.

"What makes this new is that Europe has spent a long time since the Cold War thinking it lives in a safe world," said Robin Niblett, director of the Chatham House research group. "Now it finds itself in the middle of an incredibly dangerous neighborhood."