It will only win because of the devastating firepower of the US-led air forces and sheer weight of numbers. But the fight for the city is militarily and politically complex. The Iraqi army, Kurdish Peshmerga, Shia Hashd al-Shaabi and Sunni fighters from Mosul and Nineveh province, which make up the anti-Isis forces, suspect and fear each other almost as much as they hate Isis.
The Western media is portraying the first advances towards Mosul as if it is as orderly and well-planned as the D-Day landings in Normandy in 1944. But in private Iraqis, who have seen many decisive victories turn out to be no such thing, are more sceptical about what they are seeing. One Iraqi observer in Baghdad, who did not want his name published, said that “the whole Mosul offensive seems to be a ramshackle affair held together by the expected high level of support from the US air force and special forces”.
At least 12 US generals and 5,000 US troops are reportedly in Iraq and they will play a crucial role in the coming struggle. The observer added: “I don’t think that the Iraqi forces, Peshmerga, Hashd and Sunni volunteers can singly or jointly take back the city without the physical and psychological props provided by the US.”
The US participation is crucial because although the Iraqi army and the Kurdish Peshmerga have been successful driving back Isis since it won a succession of blitzkrieg victories in 2014, they have relied on US-led air support. This has carried out 12,129 air strikes against Isis in the past two years, enabling Iraqi government forces and their allies to recapture cities like Ramadi, Fallujah, Baiji and Tikrit while the Peshmerga captured Sinjar. But these successes would scarcely have happened without the coalition air umbrella overhead, allowing the anti-Isis units to avoid fighting and act primarily as a mopping up force.
There are now about 25,000 Iraqi army, Hashd and other volunteers in and around the Qayyara area 40 miles south of Mosul, while some 4,000 Peshmerga are advancing from the east. The earliest part of the campaign in the open countryside should be the easiest because air power and artillery can be most easily deployed. Villages and towns, many of them formerly inhabited by Christians or the Shabak minority, on the Nineveh Plain east of Mosul are empty and can be bombarded without risk of civilian casualties.
But military and political calculations change when the Kurds reach the built up outskirts of Mosul, which may still have a million people it. They are pledged not to enter the city which is the biggest Sunni Arab urban centre in Iraq, though it used to have a substantial Kurdish minority. The Shia paramilitaries of the Hashd are also not supposed to enter Mosul because of Sunni sensitivities, but they can besiege it.
The Iraqi army has a number of experienced combat units such as the Golden Division, but these are limited in number and have complained in the past of being fought out because they are too frequently deployed. The nature of the fighting in Mosul will differ and be more difficult than in Ramadi and Fallujah, both of which were surrounded while in Mosul Isis has not been yet been encircled and cut off from the rest of Iraq. The US would probably be inhibited in employing its airpower in Mosul so the Iraqi army and its elite counter-terrorism units might suffer heavy casualties in street fighting with the 4,000 to 8,000 Isis fighters believed to be in the city.
This supposes that Isis will want to stand and fight for Mosul in a way that it did not in other Iraqi cities. Ever since it lost some 2,000 fighters, mostly to US air strikes, in its abortive four-and-a-half month siege of the Syrian Kurdish city of Kobani in 2014-15, its commanders have been reluctant to let their forces, which are overwhelmingly light infantry, fight from fixed positions that can be precisely targeted and obliterated by shelling and bombing. They might do better in Mosul, but the end result would likely be the same.
But not to fight for Mosul would be a bad blow to Isis. It contains one-third of the population under its control in Iraq. It is the heart of the “caliphate” that was declared here just over two years ago. It was the capture of Mosul by an Isis force of a few thousand defeating a garrison numbering at least 20,000 that astonished the world in June 2014. Isis leaders themselves saw their victory as miraculous and a sign of divine assistance. The loss of the city would, on the contrary, be evidence that the caliphate has no miraculous formula for victory and has gone into irreversible decline.
Yet if Isis is going to fight anywhere, it would be best to do so in Mosul where it has been long entrenched. If the Iraqi army counter-terrorist forces get bogged down in street-fighting, Baghdad might face a number of unpalatable choices. It could ask the US-led coalition to escalate the bombing, but this might be embarrassing and lead to comparisons with the Russian and Syrian bombardment of East Aleppo over which the Western powers frequently express their revulsion.
Another alternative would be for Baghdad to use the Hashd paramilitaries, but this would be seen as an anti-Sunni move. Turkey is struggling to be a player in deciding the fate of Mosul and maintaining its Sunni Arab character. It local proxy is the former governor at the time of the Isis capture of the city, Atheel al-Nujaifi, who has 5,000 militiamen trained by the Turks, many of them former policemen in Mosul. The Iraqi Prime Minister Haider al-Abadi has furiously demanded that a Turkish force of 1,500 soldiers at Bashiqa close to the front line return to Turkey and has exchanged abuse with Turkish President Recep Tayyip Erdogan.
Isis has always benefited from the divisions of its opponents and nowhere are these more glaring than in and around Mosul where so many sectarian and ethnic fault lines meet. These divisions have helped Isis survive for so long, but its savagery has also united leaders and parties who otherwise might fight each other. This is true of the Baghdad government and the Iraqi Kurds, who took advantage of the defeat of the Iraqi army in northern Iraq in 2014 to take over a swathe of disputed territories which expanded the area of Kurdish control by 40 per cent.
This shifting mosaic of different parties and interests makes the course, intensity and outcome of the battle for Mosul highly unpredictable. One way or another it looks likely that Isis will lose, but it is less certain who will win and fill the vacuum left by the overthrow of the caliphate. There are many contenders for this role, making it possible that the present battle for Mosul will not be the last.