It has taken two years of training a demoralized army, backed up by the air cover and special forces of the world’s greatest powers, for Iraq to mount an offensive to recapture Mosul from Islamic State.



Almost week into the U.S.-led onslaught, many of those running the campaign say the battle to retake the city could be long and hard. But they have also identified what they think is a chink in the jihadists' armor.



If local fighters in Mosul can be persuaded to drop their allegiance to Islamic State, there is a chance that the battle can be brought to a more speedy conclusion, and that could have major implications for the future of Iraq.



Against a background of splits and rebellions in the Islamic State ranks in Mosul, some opposing commanders believe that a successful attempt to win over those local fighters could mean the battle lasts only weeks rather than months.



Mosul, Iraq's second biggest city, is where IS leader Abu Bakr al-Baghdadi declared his Sunni caliphate in 2014, after his alliance between millenarian Islamists and veteran officers from the disbanded army of Saddam Hussein roared back into Iraq from bases they set up in the mayhem of Syria's war. Five Iraqi army divisions melted away before jihadis numbered in hundreds.



Now the battle to retake Mosul pits an unwieldy coalition of a 30,000-strong Iraqi regular force backed by the US and Europeans, alongside Kurdish and Shi’ite militias, against jihadis who have exploited the Sunni community’s sense of dispossession in Iraq and betrayal in Syria.



Not just its outcome but the political sensitivity with which this battle is handled could determine the future of Islamic State and Sunni extremism, as well as the shape of this part of the Middle East, which is being shattered into sectarian fragments.



Islamic State fighters, estimated at between 4,000 and 8,000, have rigged the city with explosives, mined and booby-trapped roads, built oil-filled moats they can set alight, dug tunnels, and trenches and have shown every willingness to use Mosul’s up to 1.5 million civilians as human shields.



Islamic State would seem to have a plentiful supply of suicide bombers, launching them in scores of explosives-laden trucks against Kurdish peshmerga fighters converging on Mosul from the east and northeast, and Iraqi forces, spearheaded by counter-terrorism units, advancing from the south and southwest.



"Mosul will be a multi-month endeavor. This is going to take a long time," a senior U.S. official said in Iraq.



CALIPHATE



Karim Sinjari, Interior Minister in the self-governing Kurdistan Regional Government (KRG) of northern Iraq, said IS would put up a fierce fight because of Mosul's symbolic value as capital of its self-proclaimed Islamic caliphate.



"If Mosul is finished the caliphate they announced is finished. If they lose in Mosul, they will have no place, just Raqqa (in Syria)," Sinjari said.



Adept at exploiting divisions among its enemies, last Friday's dawn assault by IS on Kirkuk, for example, was not just an attempt to divert Iraqi and Kurdish forces and relieve pressure on the main front.



It was also intended to galvanize Sunni Arab opinion against the Kurds, whose Iraqi peshmerga and Syrian Kurdish militia have fielded the most effective ground forces against IS.



That is why many of those invested in the battle for Mosul stress the need to break the cohesion of IS and the allegiance it has won or coerced among alienated Sunni, in Mosul and beyond.



The opportunity is there, they say.



They believe that while foreign jihadis will fight to the finish to protect their last stronghold in Iraq, the Iraqi fighters, many from Mosul itself, may lay down their arms.



“Most of the (IS) fighters now are local tribal fighters. They have some foreign fighters, they have some people from other parts of Iraq and Syria, but the majority are local fighters,” says a senior Kurdish military intelligence chief.



“If we can take this away from them, the liberation of Mosul is a job of a week or two weeks.”



FISSURES



Fissures are widening inside the IS camp, with Iraqi, Kurdish and Western sources reporting resistance in Mosul and a spate of attacks on its leaders.



Sinjari, also the KRG acting defense minister, says there is growing resentment against the group's brutality.



“There is information that many people are revolting and carrying out attacks against IS. A number of Daesh members were killed on the streets at night," Sinjari said. This was confirmed by the U.S. official but could not be independently
verified.



It fits with accounts of a recent abortive uprising against IS, led by a former aide to Baghdadi, that ended with the execution of 58 Daesh dissidents.



Crucially, more than half IS’s fighting strength comes from Sunni tribes initially relieved they were being freed from sectarian persecution by a Shi’ite dominated government in Baghdad and a corrupt and brutal army.



Some strategists believe those tribes could turn against the brutality of IS rule - just as the Sunni tribal fighters of the Sahwa or Awakening turned against al-Qaeda in Iraq a decade ago - if Baghdad guarantees their lives and livelihoods.



In Mosul, there are Iraqi tribal people in IS who pledged allegiance when the group arrived, a Kurdish intelligence chief said.



“If the Iraqis send a message and reassure these Sunni Iraqis that they will be given a second chance I think it is wise to do so, because if they put their weapons down you are definitely taking out 60 percent of their (IS) fighting force”.



The official emphasized the need for the US-led coalition’s close involvement in Mosul, especially after the experience of the recapture of Falluja, Ramadi and Tikrit, IS-held cities where refugees and local Sunnis suffered at the hands of Shi’ite militias.



In the battle for Mosul, it has supposedly been agreed that neither Shi’ite fighters nor Kurdish peshmerga will enter the city when it falls to avoid stoking a sectarian backlash.



While the anti-IS coalition has gained momentum, military strategists and intelligence officials say the closer the Iraqi forces get to Mosul, the harder it will be.



"If they decide to defend the city then it will be more difficult and the process will slow down," the intelligence chief said.



Once inside Mosul, Iraqi special forces would have to go from street to street to clear explosives and booby traps set up by Islamic State.



"The roads are very narrow. You can’t use vehicles or tanks, so it will be a fight, person by person," Sinjari said.



VILLAGES



Until now, it has been easy for the coalition to hit IS positions in deserted villages around Mosul but the air strikes will slow down once Iraqi forces get into the city.



Islamic State, Iraqi commanders say, have succeeded in the past in blocking army troops from moving against them by staging suicide attacks and rigging explosives.



But they say that would no longer be an obstacle in Mosul as the Iraqi army has recently received an effective guided missile system that destroys explosives-packed vehicles.



The Iraqi commanders say their tactic now would be to cut Islamic State fighters off from the hinterland of supporting villages then split the city into different neighborhoods.



Brigadier Haider Abdul Muhsin al-Darraji, from the army 10th division, said military units would launch simultaneous attacks from multiple fronts on Mosul, divide the city into sectors to isolate IS fighters. And with coalition air strikes the
jihadis will have little chance of getting reinforcements from the western side, which has been left open to encourage their departure towards Syria.



The difficulty is how to hit IS targets inside Mosul without causing massive civilian casualties.



"Its just like a tough surgery to remove a brain tumor," Darraji said.



Colonel Mahdi Ameer from the 9th Iraqi army division fighting south of Mosul said Islamic State had "deliberately blocked residents from leaving the city to use them as human shields and prolong the battle".



Islamic State’s enemies do not underestimate the group’s strength, which depends on experienced former senior Baathist officers and Islamist radicals willing to blow themselves up to defend their Sunni heartland.



"They are much more organized than the peshmerga and others. They have good administration, a good support system and enough weapons and ammunitions,” said the Kurdish counter-terrorism official.



The Mosul offensive will be the most important battle fought in Iraq since the U.S.-led invasion in 2003. What happens next will shape or break an already fractured Iraq.



"There are growing concerns about fixing the political peace the day after liberating Mosul," said Hoshyar Zebari, a top Iraqi politician and former finance minister.



"How will this multi-ethnic, multi-sectarian city ... be governed and run without communal conflict, without revenge killing, without a large displacement of people? That needs some political planning on how the city will be governed. It should have a strong representative governance in the city."



But the battle against radical Islamists in the region will not end with the liberation of Mosul.



"Mosul is not be the end of Islamic State or the end of extremism in this region. They will go back to more asymmetric warfare. We will see suicide attacks inside Kurdistan, inside Iraqi cities and elsewhere."