Americans are so enamored of equality that they would rather be equal in slavery than unequal in freedom.
Alexis de Tocqueville
the Mahdi will return to rule over the global caliphate.
So, essentially, think of it in terms of the Biblical End Times:
1 Thessalonians 5:3 ...'For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.'
Scary stuff. Used in the Bible to push Christians to become better people so that when the end comes they will be ready.
In these Islamic sects they look at it very differently. Imagine a Christian sect reading 1 Thessalonians 5:3 and thinking "Well, since destruction is the kick off of the Rapture, I guess we should commence with some destruction!" ... that is where ISIS's head is at, essentially. The Quran and the Hadiths are filled with similar prophecies of the end times that come before the rise of the global Caliphate. ISIS sees them as Allah's honey-do list.
Give a man a fish and he eats for a day. Teach a man to fish and he stops voting for the Free Fish party.