@Ionus,
The idea of a caliphate goes back to the beginnings of Islam, and Wahhabism (as practiced in Saudi Arabia) is a very fundamentalist version of Islam. The violence and extremism practiced by ISIS is very new, and did not exist prior to the invasion of Iraq. Even Al Qaida thinks they're too extreme.
Guantanamo Bay, the invasion of Iraq, the one sided approach to Israel/Palestine and the West's support of dictators including the overthrow of democracy in Iran have all helped to nurture radical Islam which is seen by many as the only true and constant opponent of Western hegemony.
We don't have a religious war
yet, but the likes of ISIS, Al Qaida, Vikorr, Oralloy and Coldjoint all desperately want one.