Europe has been way too tolerant especially regarding what going on in mosques or the main problem madrasas. These are where for the last 40 years under a massive funding program of 10s of billions the Saudis have promoted their hateful version of their religion, wahabism. So although many of the parents thought they were sending their children to good Muslim schools just like many think they send their children to Sunday school, they were actually being brainwashed into supporting hatred of Western values.
Europe has many different sources of Muslims due to our various empires. In the UK most are Pakistani from a few villages in the north whose members fought for the allies in WWII. It is very unfortunate that in India that a cleric had developed a form of Islam not dissimilar which then became popular in this area leaving them ripe for the beliefs promoted in the madrasas. Because of war in that area - you may have heard of the vile Pakistan Taliban, more fanatic but less ingrained than the actual Taliban whose origins are ethnic rather than religious - Saudi funded madrasas are the only form of education. As well as the madrasas in the UK, the population is continually supplemented by brides from this area who have attended these madrasas plus the village elders hold away over large swathes of their cohort in the UK. This explains a lot of the radicalism here but there any many other Muslim groups from areas all around the world but the reach of the madrasas is global.
The French who are less tolerant have even more Muslims largely from North Africa which has especially since the Arab spring have a particular problem with Tunisians who the Wahabis targetted in the chaos. The Tunisians are the largest contributors to IS in terms of foreign fighters. North Africa had until very recently mean far more moderate but notice how the Muslim brotherhood took over Egypt before the military stepped in and the Qatari, with misguided UK and US support, deposed and killed Gadaffi.
The Germans have the Turks, far more moderate at least until the evil would be dictator Erdogan took over using religion to consolidate his power base in a country which had hitherto been famously secular - not good, but secular. Of course he is the only powerful politician to use religion. At the moment in Europe despite names of parties such as Christian Democrats ruling we are mercifully free of that affliction.
The Dutch have Indonesians and the Belgians have Morrocans and Turks although they had little previous history of being raical until IS.
In fact if you look at it, it is almost as though there has been a plan (there hasn't because most of the seeds were set last century way before radical Islam existed outside the House of Saud's influence) to populate every country in Western Europe. The increase in population especially recently has been frightening but it has been largely internal rather than via immigration. No prizes for guessing which organisations have encouraged these population increases. In 30 years as much as 10% of the population in several European countries will stand at 10% perhaps in 30 more it will be 20%. Unless we stop the madrasas now and control the mosques we have a real problem on our hands.
Because of geography and history the US has been lucky but imagine if Mexico had been converted ...
Now you may have seen the House of Saud suddenly appearing to turn more moderate but under the surface its human rights record is getting rapidly worse with the executions of children increasing alarming while the US and others cozy up to it and they attempt to blame it's bad child Qatar. The effect of the change of policy in the 1970s has encouraged/forced other Muslim countries to become increasingly less moderate, hence modern day Iran and their agent Hamas and Hezbollah. The former have turned the barely Sunni Palestinians in Gaza into ones that have become more fanatically religious although not Shiite.
The reason for this was actually graphically shown in Big Brother. They put a couple of Muslims in the house. There was a moderate Muslim who was confronted by a female gang member about how he was a "Bad Muslim" and should be ashamed of himself for mixing with men lusting after white women, not praying all the time, being possibly gay and above all for drinking alcohol. The guy was mostly harmless although did get expelled for spitting in someone's face but she threatened to have him killed for bring a poor example of his faith. She was expelled for that but the "You are not a good Muslim mantra" is destroying moderates all over the place so 20 years ago there was no Muslim problem, there is now and the primary cause really isn't the numbers but the brainwashing and intimidation.
So the West should close down these schools, reintegrate the Muslim population and above all stop being friends with the Saudis. They are the true enemy of the West and yet we sell them billions if not trillions of arms! In return the Arabs leave Israel alone and persuade the US and others that Iran's is problem. Iran fought IS, the Saudis sent one female pilot over for a publicity stunt. The West is being conned. The West is fully aware of this, but in turn for selling their souls to Satan (it is a phrase, I am an atheist remember) Israel gets protected and the arms industry and certain individuals in the West through oil interests make lots of money so they don't care. Not hard to work out why Trump has cozied back up to the true enemy isn't it as almost every Western leader has done beforehand.
Actually although we know Trump does not give a fig for the Middle East except for the reasons stated, this may lead to more chaos in more Muslim countries making their citizens vulnerable to yet me Wahabi inspired radical thought and the Saudi's grand plan of expansion of influence gets another boost as it did with the second Iraq war and the Arab spring.
This is ignoring what the Arabs are doing to Africa and elsewhere in the world. Here South East Asia take lots a money and we'll look after your education system!