Terrorist attacks are horrible regardless of where they take place, and my heart goes out to anyone who is touched by this form of violence. Unfortunately these types of attacks with mass casualties where very common throughout the 70's into the mid nineties in Europe. There was a drastic drop in terrorist attacks in the mid to late 90's to the mid 2010's. (With the exception of a few large scale attacks in single European countries).
Ultimately if it is not ISIS it will eventually be someone else.