Do you think that ISIS can develop or evolve into a legitimate challenge to the existing global powers in our lifetime? Right now they seem like fractured bands of militias fighting for regional goals, but banner goal is still to establish a Caliphate. In addition to fighting, they're building schools and utilizing propaganda and have seem to build a following that's larger than originally anticipated.
There were other cases where ragtag militia groups were able to unite under a strong leadership and eventually gain enough power to challenge the existing power. Genghis Khan was able to unite the Mongolian tribes to challenge the existing Chinese dynasty. Saladin was able to unite the Muslims against the crusaders. And Mao was able to transform Communists from a small force fighting along the mountain sides into a big enough force to fight the Nationalist party.
Do you think that ISIS can or will do the same?