[psgbg]

Hmmm. "Muslim..."

This is the same with all kind of violence most of it doesn't have a reason.

But in this case it has. In the case of terrorism it's a business. Their goal it's to stablish an image and get the people that might oppose them prefer to do not intervene. And the people they want submission be that submissive. With this they can exercise control. Impose authority, sell protection (for example) and control any kind of illicit activities.

It's the same with the drug cartels like "The knights of Sinaloa", the organized crime remember the "Cossa Nostra". The mongols to cite an old example.

Conquer by fear.

To end it, well that's another issue. You need to end their flux of money. Cut their recruitment systems. End the fear.