In fact, the problem is even more specific to western propaganda created purposefully to create a Yinon outcome in Syria: "Terrorism in Europe: how US and Western governments nourished and encouraged Al-Qa`idah terrorists in Syria":
"You can really trace the current problem of terrorism hitting Europe to the beginning of the Syrian war in 2012 and the insistence of Western governments--against all available evidence--on creating the myth of "moderate Syrian rebels". Western propaganda glamorized a non-existing Syrian "revolution" and romanticized those Muslims in the West who took the trip to fight with the various Jihadi group. The myth of the moderate Free Syrian Army was in full swing at the time, and any opinion which warned of the dangers of rise of terrorist groups in Syria was immediately dismissed as pure Syrian regime propaganda. The dangerous propaganda ploy of Western media continues. Look at this map from this article in Bloomberg. Look how the areas designated as "Syrian rebels" is so widely expanded. In fact, if you look at the areas around Idlib, the dominant force there is Nusrah Front even if it works with other militant Jihadi groups under the banner of Jaysh Al-Fath. So basically, whenever Nusrah Front (the descenents of the terrorists of Sep. 11) align themselves with other rebel groups, Western propaganda and media outlet regard the rebels in that area as "moderate Syrian rebels" because they are not fighting under the banner of Nusrah although the banner exists. This is one of many example but it gives you an idea. And Zionists have been most active in this regard and in spinning this propaganda but they are not alone: some liberal and leftists have also been spinning this fable."THE BELGIAN SYNDROME: From Rear Base to Front-Line State for European Jihadis"
PS This article by the research arm of the Israeli lobby concedes the point about Nusrah Front in Idlib."
Brussels is where NATO is. It is a staging ground for the European dupes who fight for ISIS in Syria, with the police and other authorities turning a blind eye to their presence and activities. Extreme violent Islamist sects are now part of the NATO arsenal, so they are not just tolerated, they are coddled. Usually you don't shit where you eat, explaining the relative calm in Belgium, but the perceived betrayal of the European elites has prompted violent revenge.