Source Stratfor:

There are simply too many red lines for the region’s Sunnis. Even in the unlikely scenario that Saudi Arabia weakens so much that Iran assumes de facto control of the Arabian Peninsula, the Sunni populations would not allow the holy cities of Mecca and Medina to remain under Shiite control. And there are simply not enough Shiites to do anything about it since they are essentially surrounded by Sunnis.

In addition to religious considerations, there are also ethnic considerations that prevent the spread of Shiite rule. Shiite leadership is now in the hands of Persians, not Arabs. And though Arab Shiites have aligned with Tehran, they have done so only out of necessity, maligned as they are in their respective countries. This limits the extent to which Iran can rely on them to serve its purposes.

Though the Shiites of the Arab world have largely united, some of their differences will be very difficult to ignore. Competition still exists between the Iraqi theological centers of the Arab-dominated Najaf school and the school in Qom, and Tehran has tried hard to increase its influence over Najaf. Iranian leaders hope that the power vacuum in Iraq will enable them to spread their doctrine of Velayat-e-Faqih. But with Iran undergoing its own political transformation, tensions between liberal and conservative factions – and between democratic and theocratic factions, considering the rise of Iranian President Hassan Rouhani and the domestic rehabilitation he began – have become more acute. Those tensions could well command Iran’s attention, leaving its international aspirations by the wayside.

Thus, as much as Iran would like to further exploit current Sunni weaknesses, changes underway in Tehran could thwart its leaders’ regional ambitions – as could internal differences among Shiites and the progression of the Syrian civil war.

More: