The Islamic State in Iraq and the Levant (ISIL) organization swept into the city of Mosul in western Iraq last week. No one has any right to be surprised. ‬

ISIL has held a large swath of western Iraq since January – including the city of Fallujah. The organization was clearly planning a larger scale offensive action into Iraq. ‬

In January it had carried out a strategic withdrawal from large swaths of Idleb and Aleppo provinces in Syria. This was intended to consolidate its lines in northern Syria, so as to move fighters out toward Iraq. ISIL controls a contiguous bloc of territory stretching from western Iraq up through eastern and northern Syria to the Turkish border. ‬

Its “Islamic State” is already an existing, if precarious fact, no longer a mere aspiration. So, like a state at war, it moves its forces to the front where they are most needed‬.

The rapid collapse of Nouri al-Maliki’s garrison in Mosul in the face of the ISIL assault should also come as no surprise. These forces are hollow. ‬

Saddam Hussein maintained a huge army by coercion. Shirkers and deserters could expect to be executed. But Maliki’s army consists of poorly paid conscripts and often corrupt officers. The Shia among them in Mosul saw no reason to fight and die for what seemed to them to be Sunni, alien territory. Sunni officers among the garrison, meanwhile, may well have been working with ISIL itself or with one of the other Sunni Islamist or nationalist formations fighting alongside them. ‬

So what will happen now? The pattern of developing events is already clear, and much may be learned from the experience of Syria. ‬

Bashar Assad, when rebellion broke out against him in March 2011, sought to use his huge conscript army to crush it. But the Syrian dictator rapidly found out that his supposedly 295,000-strong army was largely a fiction. Sunni conscripts refused to engage against the rebels, and Bashar was able to make use only of certain units composed largely of members of his own Alawi sect – units such as the Republican Guard and the 4th Armored Division. ‬

How did Assad address this problem? The answer is that he didn’t – Iran did. ‬

Realizing that their Syrian ally was facing defeat because of an absence of reliable manpower, the Quds Force of the Iranian Revolutionary Guards Corps stepped in to effectively create a new, sectarian military for the Assads. In addition, Iran introduced its various regional paramilitary proxies into the Syrian battlefield. ‬

By mid-2013, the new, sectarian infantry force trained by the Quds Force and Hizballah – named the National Defense Force – was beginning to be deployed against the Syrian rebellion. In addition, Hizballah, and Iraqi Shia volunteers of Sadrist and other loyalties began to fill the gaps in manpower for Assad. ‬

These units turned the tide of the Syrian war. But they have brought Assad survival, not victory. The dictator rules over only about 40% of the territory of what was once Syria. The rest is under the control of ISIL, the Kurds, and the Sunni Arab rebels. ‬

It is likely that a similar pattern will now emerge in Iraq. Quds Force commander Qassem Suleimani has been in Baghdad since Friday. He is in the process of organizing Iraqi Shia volunteers, who in the months to come are likely to be transformed into a sectarian military force resembling the Syrian National Defense Force. ‬

In addition to the new volunteers, Iraqi Shia militiamen in Shia southern Iraq and in Syria are flocking toward the battlefront, eager to do battle with ISIL on their home soil. ‬

These hastily assembled forces, along with the reliable elements of Maliki’s military, are likely to prove sufficient to defend the capital and perhaps to prevent further gains by ISIL, which may have over-reached itself. But the new, openly sectarian Shia forces behind Maliki are unlikely to succeed in re-taking the entirety of ISIL’s territorial gains in Anbar and Ninewah provinces. ‬

Iran is a leading world expert in the creation of proxy sectarian military forces. But given the demographic balance in present day Iraq, and in Syria, Iran’s assistance is likely to ensure the survival of the non-Sunni population only in a part of the country in question. That is – ISIL and Iran’s intervention into Iraq may well portend the de facto partition of that country, and its plunging into a prolonged conflict, along the lines of what is currently taking place in Syria. ‬

Indeed, given the players engaging in Iraq, it is more sensible to see the Syrian civil war and the renewed Iraq conflict as different battlefronts in a single, sectarian war – in which Sunni and Shia/Alawi forces are clashing. The latter are backed crucially by Iran. The former receive far less systematic and determined backing from a variety of sources, including private elements in the Gulf and perhaps the intelligence services of a number of Gulf states.

Only in Lebanon, which lacks a native Sunni military tradition, have the Iranian proxy forces managed to secure near complete military domination of the country. In the very different and far more consequential contexts of Iraq and Syria, Sunni rebellion and Iranian reaction are likely to produce the fracturing of the countries in question along sectarian lines. ‬

The Kurds, possessors of a strong, largely secular nationalist tradition and identity, may emerge as major winners from this process of fragmentation, in the context both of Syria and Iraq (as witnessed by the rapid gains made by the Iraqi Kurdish Peshmerga forces in recent days). ‬

As for the warring Arab Islamic sects, they are set to continue to battle one another, with ready foreign help, over the ruins of the countries once known as Iraq and Syria. This war is just beginning. Any attempts to portray either of the warring sides as “anti-terrorist” or “pro-western” should be stubbornly resisted. Acceptance of such definitions is the entry hall to new policy failures and wasted lives. ISIL and the Quds Force differ in organizational structure, but are similarly anti-western – and similarly vile. They should be left to bleed one another white.‬

Jonathan Spyer is a senior research fellow at the Global Research in International Affairs (GLORIA) Center and a fellow at the Middle East Forum.