So this thing is degenerating into a Shiite vs. Sunni war that could easily turn into a massive region-wide conflagration. Recently ISIS said they were going to destroy Mecca.
I'm sure the Saudis will do everything they can to end the threat to the place that they are supposed to guard with everything they have. What I have been thinking is that this might be the first shots fired in what could be The 30 Years War of Islam. This book on the 30 Years War is what got me thinking.
The 30 Years War started in 1617 and was basically a number of Catholic powers fighting against a number of Protestant powers. It was the last major all-out war of the Reformation basically because it was terribly destructive and resulted in hideous tortures. Some states in what is now Germany and Czech Republic were nearly wiped out and others suffering 30-40% losses. Some sources say that 50% of all the men in the German states were killed. It strikes me that an all-out war between the Sunni ISIS and the Shiite Iranians, Saudis protecting their holy sites and the Iraqis might be a similar conflict.
In fact we have may of the the parts already in place. We have bloodthirsty zealots on one side and an army that can give no quarter on the other. All we need are foreign mercenaries (gulp, maybe that is the USA?) to come in and start fighting to have us back in 1617 again.
During the 30 years war we start with battles in Bohemia (Syria) then Spain intervened (that might be Sunni zealot part of the Middle East.) Then we have the Danish come in on the side of the Protestants (that might be the Saudis protecting their holy sites) Then the Swedes come in on the side of the Protestants (this would be Iran.) Finally France came in at the end (that would probably be Turkey since the French were mostly fighting the Hapsburgs and not the Catholics as a group.) We might even see the birth of the Dutch Republic (that would be Kurdistan.)
I'm sure if the Iranians enter the war in any numbers they might be able to sweep the field of ISIS but not before we might see some serious bad things happen. ISIS now has some uranium so a dirty bomb can be cooked up and used on Baghdad or perhaps Tehran. That would seriously push Iran and Iraq closer together. Also if I was Iran in "the Great Game" I would conclude a status of forces agreement to garrison troops in Iraq so an ISIS can never form up again. What would be really bad for Islam is an ISIS suicide bomber could blow up something in Mecca. So many pilgrims pack into places like the Ka'aba or Mina that a bomber could easily kill 10,000 people or more from an explosion followed by a stampede.
In any case history doesn't usually repeat itself but every now and then it sure rhymes.