From Ben Reynolds:
….No one is innocent in the Iraqi and Syrian civil wars, but Iran is not primarily responsible for the current state of affairs. The U.S. and its allies destabilized Iraq and Syria in turn, creating safe havens for extremists that previously did not exist. U.S. allies provided the material support that allowed ISIS and groups like it to become threats to the entire region, despite lacking any substantial popular base in Syria and Iraq. It is not unreasonable for Iran and Hezbollah to fight against these groups, which murder and enslave Shia and other religious minorities. Their actions conceivably fall under one of the West’s favorite principles of international law: the duty to protect.
Read more at Iran Didn’t Create ISIS; We Did | The Diplomat.