the enemy of my enemy is my friend

StrategyPage has a long analysis of the ISIS rebels, whose extremism is uniting both Iran and Saudi against them (and will result in the more moderate Syrian rebels to lose their fight for freedom). The ISIS is mainly from the desert tribes...

 the Saudis and Iranians have to pause their growing Sunni-Shia feud because both countries have more to fear from ISIL Sunni Islamic terrorism than from each other. Western nations know they are already on the ISIL radar and are cracking down on ISIL fund raising and recruiting in the West. Where does this leave the Syrian rebellion? The secular rebel groups and acceptably moderate Islamic rebels already have a coalition of sorts although that currently includes unacceptably radical groups like al Nusra. In short, things do not look good at all for the rebels. They are screwed.

they also note 160 thousand casulaties of the Syrian rebellion so far.