The whole religion thing is largely nonsense. Not a single religious authority outside the IS itself, not even the extremely radical Wahhabists or Al Qaeda itself considers the IS to be genuinely Islamic. The IS remind me of some of the most brutal nihilist fighters of the Spanish civil war, those who reveled in the virile energies of anarchy and the absolute power of their arms. They were hiding behind communist, fascist or anarchist ideologies which were mere excuses. Many joining from other countries looking at first to fight for their ideals ended up reveling in their hormonal addiction.
The extreme violence of IS makes Iraqis react with an almost pavlovian fear. It is the sign of their old masters who conditioned them to cower. It is how Saddam Hussein kept Iraq under control of his clan and for decades reinforced the message that death can be imminent and unpredictable even to those who do obey. I’m glad an analyst finally firmly points towards how the IS has co-opted former regime elements. But there’s more: the IS also understands how to tactically defeat armies like the Shi’a Iraqi army and the Peshmerga. Plus, the level of experience shown at administering large areas and huge cities points at substantial executive experience and substantial administrative networks. The IS has captured and still hold Fallujah, Ramadi, Tikrit and Mosul. And those who paid attention all realize to what degree Saddam’s loyalists are from these cities (Saddam’s clan is from Tikrit).
But the hold of the IS itself on power is divided; it is based on extreme violence on the one hand and on a solid administrative capacity on the other. These cannot coexist for long. The coexist because the Sunni have no alternative. The moment a mature and credible alternative presents itself, the extremely violent brigades of the IS will be relegated to history. But this isn’t 2007 and the trust the Americans built up then in Sunni provinces of Iraq is not easily rewon, especially not by a largely sectarian and irrelevant government in Baghdad. Also the regime’s crackdown in Syria is directed almost exclusively at the Sunni and as long as that conflict isn’t settled, it will continue to bleed profoundly radicalized people and ideologies into Iraq.
The IS observation that the Sunnis in Syria and Iraq ought to stick together and fight what is perceived to be a common enemy is true enough, they are subject to extreme repression in both countries and they do face an enemy that has common characteristics. Their security (especially in Syria) is not at all a priority of the outside world so them joining in a common front is logical and the longer it lasts, the more solid their collective identity and narrative of resistance becomes. It then is the birth of a new nation indeed.