For the first two years of the war against the Islamic State the script for liberating Iraq’s major cities seemed set until Fallujah was freed. Tikrit and Ramadi took months to re-take and were marked by fits and spurts by the security forces. The defense in depth that the insurgents built meant slow going for the Iraqi forces, while IS units re-infiltrated into the rear for harassing attacks. That all changed with Fallujah however that fell in just weeks. The real problem turned out to be a humanitarian one. Could the battle for Mosul go down the same way?
Tikrit and Ramadi seemed to set a pattern for how the Islamic State would defend major urban areas. IS laid down multiple IED fields with covering fire from snipers on the perimeter. IS would also re-infiltrate into the towns surrounding the cities delaying the final assault. On the inside of the cities there were booby-trapped houses and tunnel systems so that IS fighters could maneuver without being exposed to Coalition airstrikes or Iraqi artillery and mortar fire. It also allowed the militants to come up behind the Iraqi forces in surprise attacks. Finally, multiple suicide bombers and car bombs would be launched to break up Iraqi units. The Islamic State didn’t have the numbers to hold these areas, but they were able to drag out the fighting for months and cause thousands of casualties. Ramadi for example, took four months to be freed. Half of that was spent just getting into the city and then the other half to clear it. What allowed the Islamic State to build up such defense in depth was the fact that Tikrit and Ramadi had basically been emptied of their populace in the run up to the operations. With no civilians, IS was free to plant bombs and maneuver anywhere it wanted. That was not true of Fallujah.
The battle of Fallujah went down surprisingly quickly given the previous battles. The city was liberated in just five weeks. At first, it seemed like the Iraqi forces were going to have the same hard time as they did in Tikrit and Ramadi with all the IEDs and snipers, but when they were able to penetrate into the interior of the city the insurgents’ defenses quickly fell. The difference was that Fallujah was a major command center for the Islamic State. It not only maintained facilities there, but housed its families and thousands of other civilians. Because of that IS was only able to set up perimeter defenses, and little on the inside. Instead, what turned out to be the major problem in Fallujah was the humanitarian crisis that developed as approximately 80,000 families fled the militants. The government and humanitarian organizations were not prepared for such an exodus lacking facilities, supplies and money. After the battle was over their plight did not improve much either due to those same issues.
Mosul could go down in much the same fashion as Fallujah. Like the latter, IS uses Mosul as one of its two main hubs in Iraq and Syria. There are still over a million people living in the city as well. Unless they move their operations out and depopulate it, the insurgents will not be able to create the intricate defenses that they did in Tikrit and Ramadi. Instead, there will be a tough exterior and weak inside again like Fallujah. Just like that city, the real dilemma will be dealing with all the people that flee, because the government and NGOs are still not prepared for the mass displacement due to their lack of money. The political disputes between all the factions that want to be involved in the operation that are emerging now, will also play a role afterward.
The battle for Mosul is still months away. At the earliest the city could be attacked by the end of the year, but early 2017 is more likely. Liberating it could take less time than it took to get there. The Islamic State made a huge overreach when it seized Mosul in the first place in the summer of 2014. Once the Iraqi government regrouped and the U.S. led Coalition entered the fray IS was going to lose all the territory it seized in Iraq. The group is aware of that inevitability making announcements that it might lose its state, but that it will endure. The real dilemma now is what will happen in the aftermath. Over one million people are likely to be displaced during the battle and Baghdad lacks the resources to take care of them. Just as important the government doesn't have the money to rebuild Mosul either. Finally, there will be political disputes over the administration of Mosul and Ninewa in general, and likely revenge attacks as well. Those issues will all likely be exploited by IS as it tries to regroup after its losses and re-infiltrate back into the city that has been its main base in Iraq for years. Those are the factors that will have a lasting impact past the freeing of the city itself.