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...
If you don’t know why Iran would be worse, find out. They are still the world’s number one state sponsor of Islamic terrorism, and they are insistent upon starting World War III to induce the coming of the Mahdi.
And there was general unity during the Crusades against the Christian world that transcended any Sunni-Shi’a dispute about a born successor to Muhammad. That was mostly due to the numbers of Sunni to Shi’ite, but that would still apply today—especially since all of Iran’s Supreme Leaders were and are about putting all differences aside to wage jihad against the non-Muslims.