Does the Iraqi army have the right stuff to win the battle everyone knows is coming -- and handle the messy aftermath?

On Feb. 19, a senior official with U.S. Central Command leaked details about the most widely anticipated military offensive in the Arab world -- the battle to retake the Iraqi city of Mosul from the grip of the Islamic State. The official said that combat operations could begin in March or April and would involve as many as 25,000 Iraqi and Kurdish troops.

The debate that followed this announcement has mainly focused on the wisdom or logic of airing battle plans and to some extent on the feasibility of the timeline. But arguably the most important question is: How should Mosul be liberated to ensure its long-term stability? After all, if Mosul is cleared of jihadis, only to fall to the Islamic State again some months later, what's the point? What if Mosul collapses into factional warlordism akin to civil war-era Beirut or today's embattled Libyan capital, Tripoli?

Serious soul-searching needs to precede the looming battle for Mosul because it is an environment like no other in Iraq. Mosul is distant from Baghdad -- both physically and culturally. It is a 200-mile drive from the capital and 100 miles north of the nearest Iraqi military bases at Baiji, the Iraqi Army's tentative foothold in the north. Mosul is Iraq's second-largest city, boasting a population of just over 1 million people, with half the surface area of Baghdad but more than twice that of Basra, the third of Arab Iraq's traditional regional centers.

Mosul also includes a mosaic of religions and ethnicities. Its population was as much as 65 percent Sunni Arab prior to the June 2014 takeover by the Islamic State, according to election results, and is probably even more strongly Sunni now after an exodus of non-Sunni minorities in the early days of the Islamic State's control. Kurds, Turkmen, Assyrians, and a host of other minority ethnic and religious groups have long called Mosul home, but probably compose well under a quarter of Mosul's population today.

Iraqi forces will also be attacking a city where most of the civilian population remains in place. Unlike in the Islamic State-held cities of Fallujah and Tikrit, the jihadi group has actively worked to ensure that most Mosul residents remain trapped within the city. It has enforced a "guarantee system" requiring those leaving the city to designate three hostages who will be punished if they fail to return.

Due to these factors, the liberation of Mosul represents a unique challenge for the Iraqi government and its international partners. An early recapture of the city, in line with the time frame that the U.S. military official outlined on Feb. 19, remains unlikely to be realized.

This isn't the first time that the United States and its Iraqi partners are struggling to figure out how to secure Mosul. The city was previously a notable blind spot for both the U.S.-led coalition and the Iraqi government. It was never truly pacified: In 2008, a reinforced brigade of more than 3,000 U.S. troops, two brigades of Iraqi Army troops, and six smaller brigades of federal police -- a total of more than 15,000 soldiers -- only grazed the surface of securing Mosul from al Qaeda in Iraq (AQI) and other insurgent groups. Their efforts succeeded only as long as local Sunni Arab militant factions chose to limit their operations. When AQI began reconstituting itself in Iraq as the Islamic State from 2011 onward, it rebounded most strongly in Mosul, expanding its large-scale organized crime rackets and attacks on security forces.

Equally significant, it is clear that the Iraqi government cannot count on its standard formula of relying on predominately Shiite militias to recapture Mosul. The Shiite "popular mobilization units" have aided desperate Sunni tribes in some cases, but Mosul is the capital of Sunni Iraq -- a city where the Shiite-dominated security forces' June 2014 expulsion was initially welcomed by city residents. Nor can the Kurds be counted on to pour the blood of their Peshmerga fighters into a city where Kurdish units will be intensely unwelcome, particularly in its heavily Arab western side. This raises the question: Just who is going to liberate Mosul?

THE MEN WHO WOULD LIBERATE MOSUL

According to the Feb. 19 Central Command briefing, the assault force might include five Iraqi Army brigades, with three smaller Peshmerga and Iraqi brigades in support. Other reporting suggests that a follow-on gendarmerie force of Mosul policemen would be inserted into cleared areas as a stabilization force.

Under optimal conditions and with smart planning, the planned force of 20,000 to 25,000 soldiers might just be big enough. Perhaps the approach of a credible relieving force will itself cause the Islamic State's grasp on the city to crumble. In a best-case scenario, the latent militant and community networks in Mosul could begin to turn against the Islamic State, sealing off their areas and sitting out the battle. And the Islamic State might overreact and hasten its demise with acts of barbarity that spark a rolling rejection of its presence. Any of these possibilities could be accelerated by coalition airstrikes and U.S.-enabled psychological operations that take control of the cell-phone system and allow direct communications with the public. An attacking force would be well served to selectively seize symbolic locations such as Mosul's airport, the adjacent Ghizlani military complex, and even the Tigris bridges.

But attacking with such a small force represents a dangerous gamble. Iraq's post-Saddam military has never undertaken such an ambitious endeavor as the recapture of Mosul. Unless the Islamic State's determination to hold Mosul is far more fragile than anticipated, an assault force of fewer than half a dozen lightly manned brigades could quickly be ground down by the jihadis. The mooted 25,000 troops might appear to have much more than the traditional three-to-one advantage required to attack, but in reality the sheer number of military tasks faced by such a force would quickly soak up and wear down the liberators. In every area of the sprawling city, the security forces would need to defuse dense patterns of booby traps, clear buildings, screen military-age males, and restore stability and services. And getting back into Mosul may be the easy part.

THE POST-ISLAMIC STATE IN MOSUL

Mosul is the first battlefield in Iraq where all three major ethnosectarian blocs will converge upon one city, bringing their own agendas into the operation. Do the Kurds want the Iraqi Army back on their doorstep? Do local Sunnis want a new flood of strangers from Shiite southern Iraq policing their city? What happens if Shiite militiamen and volunteers enter the fight or if any of the liberating forces begin to punish suspected Islamic State collaborators within the population? Does the incursion occur in such a way as to splinter local Sunnis from the Islamic State or drive them together?

These questions matter because Mosul's Sunni population has the muscle to determine the city's fate. Thus far, with no help in sight, anywhere from 2,000 to 6,000 Islamic State fighters have dominated the city's population. But there are probably well over 100,000 military-age males in Mosul with AK-47s in their closets who haven't picked sides yet and are waiting to see what the government can offer them to fight the Islamic State. They have been betrayed by Baghdad before and will need strong reassurance, backed by the international community, that they will not be reoccupied by security forces alien to the city. But if the Iraqi government can assuage their fears, they could still yet join the fight against the Islamic State.

Another unknown is how the Islamic State is preparing for the "day after" the recapture of Mosul. The city is probably too large an area for the Islamic State to fully prevent a liberating force from entering, so how will the group defend it? Will it abandon Mosul for good, or will it reappear there again in the weeks and months after liberation? The city of Ramadi, another Sunni stronghold, offers a disturbing potential comparison: An urban seesaw struggle has persisted there for more than a year now. Might the Islamic State be able to maintain a similar persistent campaign of localized counterattacks in Mosul if the security forces are alienated from the population, are overstretched, or are inadequately supported by Baghdad and its international allies?

All this suggests that retaking and achieving basic stability in Mosul will be a more complex and lengthy process than anticipated. Prime Minister Haider al-Abadi hinted at this reality on Feb. 16 when he said that Mosul could be liberated within three to five months or "longer."

It won't be easy, and it may not be quick. But retaking Mosul is an endeavor that is worth undertaking -- and worth doing right. The Islamic State's grip over Iraq's second-largest city has been a symbol of the movement's success. Mosul may be the one battle in Iraq that can decisively prove that the Islamic State is a losing cause.

Michael Knights, a Lafer Fellow with The Washington Institute, travels to Iraq regularly to work with local leaders, government ministries, and security forces. Michael Pregent was an embedded advisor with a Peshmerga battalion operating in Mosul in 2005-2006. He also served as a Defense Department advisor on the Iraqi security forces from 2006 to 2011.