Terrorist attacks since 9/11 have largely been politically motivated, to use terror to get political power by violence (because peaceful means don't work for them.) It was the same with the vile Crusades. Land and power-grabs were being made by Muslims out to conquer the world. When the West (mainly Christian) stood up to try to stop them, it was all about political power. The religious element was certainly there, but the bottom line was who would control the political landscape, because once they got that, the religious aspect would follow.
Granted, it is horrific that people are terrorists in the name of their god. But that just goes to prove that their god is viewed by them as a terrorist who approves of his followers using terrorism to force their goals and beliefs on to others. And if they won't accept their politics and religion, they will decapitate them, or stone them to death, or shoot them, or blow them up with bombs.
The two World Wars used terrorism all the time. Political reasons were at back of them, however, not religious convictions. All wars use terrorism. Why should anybody be stunned when a terrorist group also claim religious excuses? It's all girst to the mill, for them. Truly, the children of the devil are clearly identified by that. Just thank God there are millions of Christians who never, ever use, or excuse, terrorism. They are not in any one political party, or any one denomination, however. But there are millions who would rather be killed than kill - who would rather preach the gospel of peace than the politics of terror. (You do realise, of course, that the one man who terrorised those Muslims in N.Z. was not a religious person - he was extreme right-wing, politically.)