The conflict in Mosul is again, for the first time in four months, dominating western media headlines. On that occasion, the Iraqi government forces were launching their effort to dislodge ISIS from eastern Mosul. It was expected to be a relatively quick and straightforward military operation. By the end of the year, the whole of the city, both east and west of the Tigris, would be freed. In reality, the stalling of initial progress and bitter house-to-house fighting meant more than two months were needed to control just the city's east.

Two factors handicapped the offensive. ISIS forces were very well prepared to defend their territory, not least through around 5,000 operatives able to work through an extraordinary network of tunnels. And though the Iraqi troops numbered 60,000 or more (against ISIS's approximately 5,000), only the elite units known as the counter-terror service (CTS) or “golden division”, perhaps 10,000 strong, were capable of urban counterinsurgency against a determined enemy.

In the event, even that force suffered serious casualties over the two months. This, as Politico reports, could have long-term implications for Iraqi security:

“With the division suffering “horrific” casualties every day, senior US Centcom officers are worried that the grinding battle is slowly destroying the division itself. If that happens, which appears likely, Iraq will lose its best guarantee against civil war – the only force capable of keeping the peace when Iraq’s sectarian divisions, temporarily dampened by having to fight a common enemy, re-emerge” (see Mark Perry, "How Iraq’s Army Could Defeat ISIS in Mosul—But Lose Control of the Country", Politico, 15 December 2016).

Baghdad's eventual capture of eastern Mosul in January 2017 was followed by a month's hiatus while preparations were made to move against western Mosul. Even then, ISIS activity – often well behind Iraqi lines – has continued. After all, surviving ISIS forces had gone to ground. Moreover, the Iraqi government-approved militias (largely Shi'a) that ruled much of the city after the CTS had done its work have been acting violently against the city's Sunni residents. This unstable situation, repeating the pattern of previous areas recovered from ISIS rule, augurs badly for an end to the conflict.

The sectarian factor is vital, for the government of Iraq's prime minister Haider al-Abadi is hugely dependent on the almost wholly Shi'a "popular mobilisation forces" (PMF), which number around 100,000 and have close links with Iran. PMF units have been prominent throughout the campaign against ISIS. Without their role – as well as extensive air power and training support from the Americans and their allies (British, French and others) – Baghdad would have made very little progress against ISIS in the past year.

Iraq in the balance

This carries a major implication for what is likely to happen "after Mosul". The operation to take western Mosul will again be fierce   and likely result in high civilian casualties. Eventual Iraqi government success is probable, with the reported capture of the city's damaged airport on 23 February being hailed as a breakthrough. The whole operation may again take months rather than weeks. But whenever victory is declared it will be the prelude to other major problems, especially as the PMF units increase their influence in the city.

Indeed, PMF forces have for several months been fighting ISIS in the villages west of Mosul towards Tal Afar. They are currently engaged in expanding their control in operations that appear to be coordinated with government actions. 

Given these difficult circumstances, the least worst outcome now could be for the ISIS leadership to withdraw from Mosul as a lost cause. That would minimise civilian casualties in the short term. After that ISIS might decide to engage in a largely hidden insurgency. But on the political side, the Baghdad government could use the space to make a determined attempt to reach out to the country’s Sunni minority, offer it concessions, lesson its suspicions, and in the process undercut support for ISIS.

The regrettable reality is that ISIS will almost certainly fight for as a long as it can, exact the heaviest casualties on the CTS and leave al-Abadi even more dependent on the Shi’a militias of the PMF. If that happens in the battle for Mosul, another element will come into greater prominence: the direct engagement of United States forces in ground-combat.

Since 2014, American troop deployment in Iraq has risen steadily to around 5,000. Most have been in training roles, though there are sizeable special forces and also marines involved in artillery-support. Today, a much expanded US military presence in the region means that the number of personnel involved in the air war is probably heading towards 20,000.

Furthermore, military sources are sending clear signals that the US should also increase its direct participation in the anti-ISIS fight in Syria. The head of US forces in the region, General Joseph L Votel, wants more troops on the ground to support the eventual assault on Raqqa (see Michael R Gordon, "More U.S. Troops May Be Needed Against ISIS in Syria, a Top General Says", New York Times, 22 February 2017).

It is now being reported that, since Trump's election, US troops are more likely to be involved directly in ground-combat, including 500 committed to the campaign to drive ISIS from western Mosul. This may seem a small issue but the political significance is considerable, not least because it means the ISIS propagandists can more easily promote their mantra that the “far enemy” is attacking Islam on the ground. If US intervention grows in size and visibility, echoing previous engagements in Iraq and Syria, that narrative will sharpen.

Much depends on how Trump's campaign pledge to crush ISIS will be implemented. In any event, a relentless US-led air war as well as the fighting in Mosul will continue to put ISIS under heavy pressure. But the troubled efforts to take the city show that it is still has assets in store.