Every time we hear about an attack credited to ISIL we need to take a look at what is really being said. Is the attack "inspired"/ "motivated", by ISIL propaganda or is the attack "conducted"/"coordinated" by ISIL. It's important to note the two are not the same. The Attacks that are inspired/motivated by ISIL show us the organization is expanding through media and where they are being most effective at it. Their goal through the attacks that are committed for these reasons is to maximize the creation of havoc and fear in the world at large. Through these acts it is hoping to create an apocalyptic event which will leave the Caliphate as the controlling organization of the world.
They claim responsibility and incorporate these acts into their propaganda to have the appearance of expansion for this reason.
If we look at where ISIL is known to be responsible for the acts committed we find it is in a concentrated area. With the exception of a handful of attacks to include the attack in Paris, France all ISIL attacks have occurred within the Middle East and North Africa. The rest of the attacks are attacks in which the perpetrator was "inspired" or "motivated" by ISIL.
A part of our strategy should be preventing ISIL from conducting more attacks by whatever means is necessary. Pursue their leadership, pursue their finances, confine them to operating inside a smaller and smaller area, take out their communications,...
I encourage you to look at the attached link.