It will be interesting to see what the long-term reaction will be of European nations to another terror attack on their continent. Brussels and Paris have now seen two such incident each in the past two years. Plus the London Bombings of 2005 and a laundry list of smaller-scale attacks and lone-wolf incidents have nearly every country on edge. Add to that the seemingly endless stream of Syrian refugees trying to settle in the same countries, and you have a recipe for ugly backlash.
We hear all the time from the growing Socialist movement here in the US about how we need to be "more like Europe" when it comes to our social mores and operation of government. But those Socialists may want to see what happens next in their beloved Social Democracies of the Old World.
Remember, religious freedoms--while certainly tolerated across the continent--are not codified the same way they are here in the US. There is no "First Amendment" spelling out limits on governmental control of the practice thereof. In fact, the European Convention of Human Rights clearly spells out that the practice of a religion can be curtailed if it is deemed to be a "threat to public safety and the protection of public order". How long before citizens of countries terrorized by one certain religion decide that it constitutes such a threat?
Far less open immigration policies could be tightened even more. A number of eastern European countries won't even let Syrian refugees cross their borders on board trains or buses bound for other countries--out of fear that they may get off before reaching their final destination. You laugh at a wall along our border with Mexico? There are thousands of miles of barbed wire fences all across Europe already.
And the highly homogenous societies of Europe will close ranks around themselves even more. You know why Belgian and French authorities had so little intelligence on the attackers the past few years? Probably because their is practically no assimilation of Muslims coming to those countries into the society at large. And no matter if they were born in Paris or how well they speak the language or how rude and snooty they may become, those Muslims will never be considered "French".
If you think the rhetoric of Donald Trump is "scary" here in the US, just wait until about 15 Trumpkins starts their call to rid the European continent of the "threat of Islam" in 15-different languages in the months and years to come.