Iraqi security forces in Mosul comprised a full Iraqi army division supplemented by a federal police motorized division. When these forces folded in the face of a few thousand fighters, that collapse quickly spread to units directly to the south. Nearly the entire composition of the Nineveh and Tigris operational commands began a full-scale, unorganized retreat. The drawback involved three Iraqi army divisions, a federal police division and regionally deployed police battalions — a total of as many as 30,000 soldiers. Militants quickly expanded their presence south and slightly east, facing no serious organized resistance until Kirkuk, where Kurdish security forces, known as peshmerga, had established control and contained the Islamic State in Iraq and the Levant's eastward movement. The militants' southern advance finally ran into the Iraqi army — and, reportedly, the Islamic Revolutionary Guard Corps — near As Samarra.
The Iraqi army officially had a standing strength of around 200,000 personnel until recent events, and what remains is probably not as fragile as the northern units. These units had struggled with multiple structural and systemic issues. They were stationed in what was consistently the most violent area in Iraq outside of Baghdad for several years — places where ambushes, improvised explosive devices, rockets, mortars and suicide attacks occurred almost daily, often targeting Iraqi forces.
The ethnic and sectarian balance of these units was not as predominantly Shiite as in other central or southern units; they attempted to incorporate more of the local populace, leaving them with higher percentages of Kurds and Sunni Arabs. Their area of operation rests on the eastern edge of the Sunni Triangle, the heart of Sunni resistance in Iraq, where the Iraqi army, run by the Shiite-dominated regime in Baghdad, is viewed more as an occupying force than a friendly, stabilizing element. Morale was low, desertions were rampant and the force was undermanned, so it is no great surprise that the northern units rapidly unraveled, even facing a numerically inferior force.
The majority of elite units — predominantly Shiite, better equipped and more fully manned — and of special operations forces are now centered near Baghdad or are on their way there. The lightly armed and highly mobile Islamic State in Iraq and the Levant forces and their supporters will not be able to attack Baghdad by conventional means, especially if elite Islamic Revolutionary Guard Corps units well accustomed to this type of warfare have been added to Baghdad's combat power.
The only attacks the Islamic State in Iraq and the Levant will manage with any consistency in Baghdad — and even as far south as Basra — are insurgent-style maneuvers carried out by small networks using improvised explosive devices and suicide raids. The group's conventional offensive will be contained largely to the Sunni regions of Iraq, and the Iraqi army, perhaps with foreign support, will slowly reclaim territory north of the capital.