Kenneth M. Pollack over at Brookings has provided an illuminating account of the nature of the threat facing Iraq from the recent military successes of the Sunni coalition fighting under the “ISIS” banner. The report is worth reading in its entirety, but here’s a good excerpt:
These [ISIS and other Sunni militants] are Militias First and Foremost, Terrorists only a Distant Second. Here as well, Prime Minister Maliki and his apologists like to refer to the Sunni militants as terrorists. Too often, so too do American officials. Without getting into arcane and useless debates about what constitutes a “terrorist,” as a practical matter it is a mistake to think of these groups as being principally a bunch of terrorists.
The problem there is that that implies that what these guys mostly want to do is to blow up building or planes elsewhere around the world, and particularly American buildings and planes. While I have no doubt that there are some among the Sunni militants who want to blow up American buildings and planes right now, and many others who would like to do so later, that is not their principal motivation.
Instead, this is a traditional ethno-sectarian militia waging an intercommunal civil war. (They are also not an insurgency.) They are looking to conquer territory. They will do so using guerrilla tactics or conventional tactics—and they have been principally using conventional tactics since the seizure of Fallujah over six months ago. Their entire advance south over the past week has been a conventional, motorized light-infantry offensive; not a terrorist campaign, not a guerrilla warfare campaign. [emphasis original]
Here is recent map of the situation from The Economist: