Basically it's a Civil War in Islam.
Except in Iraq (different reasons), the Shiites and Sunnis coexist with no problems. Both sects loath the Wahhabis and the fundamentalist Sunnis (al Qa'eda, Moslem Brotherhood, etc.)
If an inter-war rid Islam of these (minority) factions, which is very plausible, then the WoT is won almost without us firing a shot, so to speak.