If history is any guide, ISIS will encounter opposition from other elements within Islam and, despite its troops and its wealth will find itself under attack from those elements that want to remain the leading powers, both nationally and from non-state factions. The best course of action should be to let the Sunnis and the Shiites sort it out as they have for more than a millennium of savagery against one another.That is not what history shows as a guide. There would have been no Crusades if any of that were true, and certainly no Caliphates.
The war for Succession to Mohammed was the fight that divided Sunnis (followers of Abu Bakr - father of Mo’s last wife)) and the Shia (followers of Ali, Mo’s son-in-law). The Sunnis won hence the current leader of ISIS calling himself abu-Bakr.
I don’t know why Iran would be any worse than Pakistan or Saudi Arabia. In fact, I am sort of hoping that the entire thing breaks down in a Sunni-Shia war with Turkey staying out of it. I would love to see the Saudis (15 of the 19 hijackers) catch a boatload of hell.
Of course, there won’t be any Christians left in the ME. Even the Israelis should consider moving...