People need to realize that these attacks will not stop. They may be perpetrated by ISIS, Al Qaeda, Boko Haram, Al Shabab, Abu Sayyaf, and on and on. The common element is Islam and its theology. Because the Quran and the Hadith teaches to kill unbelievers (except for those who have been subdued and by a "street tax" called the jizya), this won't end unless Sunni Muslims either leave Islam or reject orthodoxy and adopt a reformed version of Islam. There are also other versions of Islam, such as Sufism or Ahmadiyya forms, but the vast majority of Sunni reject those as heretical. Obviously the Shi'a form that's dominant in Iran and parts of Iraq and Syria has its issues, but it doesn't commit acts of terrorism like radicalized Sunnis.

The point is, the political authorities need to look at the cause of the problem instead of just looking at the symptoms if they want to seriously deal with fixing it. Along with what I wrote, radicalized Islamist neighborhoods like the well-known one that exists in Belgium can't be allowed to continue to exist. Europe needs to be firm in stating that broad Shari'a (where Muslims not only practice Islamic law on themselves but try to force it on others) can't be allowed to exist in their countries. This means expelling the radicalized Muslims and their enablers. Saudi-funded schools that teach Wahabbi Islam have to be shut down. And Germany needs to fire Angela Merkel for leading the way in bringing in more radicalized Sunni Muslims and putting her own people at risk. Europe's weak response will just continue to invite more acts of terrorism.