The battle to retake Mosul from the so-called Islamic State in Iraq and Syria (ISIS) began several weeks ago.
The battle to drive Syrian rebels out of Aleppo has been going on for more than four years.
Although both battles are components of the complicated conflict raging across Syria and Iraq, the tactics employed by the attackers differ dramatically and reflect not only different doctrines of how to fight insurgents, but also different views about the future of the two countries.
Backed by U.S.-led coalition airpower and ground support from the United States and Turkey, Kurdish peshmerga forces and Sunni tribal units are pushing toward the city of Mosul from the north and northeast while Iraqi regular army units and predominantly Shiite militias are entering the city from the south and southeast.
ISIS fighters in Mosul could still escape to the west, as some already have, although Iranian-backed Iraqi militiamen are reportedly moving to cut off the road from Mosul to Raqqa, the ISIS's capital in Syria.
This raises a strategic question. A great many of ISIS's combatants are foreign fighters — jihadist volunteers who have flocked to ISIS from around the world. If the Islamic State falls — that is, if the territory it holds is recaptured — its leaders and local fighters can shave their beards and continue their armed struggle underground, as they did for many years in Iraq, and as most military analysts suspect they will do again.
But this is not an option for foreigners who can easily be identified. The foreign fighters must flee to other jihadist fronts, risk returning home or fight to the death where they are.
All three possibilities are happening.
From the perspective of the countries whose nationals have joined ISIS by the thousands, the return of these fighters from Syria and Iraq raises the danger of new jihadist uprisings and more terrorist attacks. These countries might prefer to see as many ISIS fighters as possible corralled and captured or killed in Iraq and Syria.
But closing the ring, leaving an army of ISIS fighters in Mosul with no options but to surrender or die fighting, will only increase the difficulty of retaking the city.
Abu Bakr al-Baghdadi, the self-proclaimed leader of ISIS — who reportedly left Mosul before the battle — has ordered the estimated 3,000 to 5,000 ISIS fighters who remain in the city not to retreat, but to wreak havoc on the advancing enemy.
Urban warfare is difficult and destructive. A small number of dug-in, determined defenders can impose heavy casualties on any attacking force. With months to prepare, ISIS has dug bomb shelters and tunnels, planted mines and booby traps, and can use civilian hostages as human shields.
The second battle of Fallujah in 2004 was the bloodiest battle in the Iraq War. In taking the city back from 3,000 to 5,000 insurgents, highly trained and well-equipped American and British forces suffered more than 700 casualties. Most of Fallujah's civilian population had fled the city before the battle began, greatly reducing the risk of civilian casualties and allowing the use of heavy firepower.
With a population that once approached 2 million, Mosul is Iraq's second-largest city. No one knows exactly how many people live in Mosul today. Hundreds of thousands fled after its capture by ISIS in 2014, and more left as the bombing campaign against ISIS escalated. The United Nations is preparing to care for several hundred thousand refugees from Mosul. Their presence imposes constraints on the use of airpower and artillery.
It is not clear that Iraqi forces would be able to sustain the heavy casualties that would come if Mosul were to become another Fallujah. Iraqi army commanders might decide to let the more fanatical militia units carry the burden of the battle.
Certainly, pressure would increase to use more airpower and artillery with fewer constraints. ISIS's well-advertised record of atrocities has eliminated any sympathy for its fighters and erodes that for the "civilians" who remain in Mosul. But a more promiscuous use of heavy weaponry poses a different set of risks.
The battle for Mosul cannot begin to closely resemble the battle of Aleppo, where Syrian government and Russian forces appear unconstrained in their application of firepower, even deliberately bombing and shelling civilian targets, which the United States and its allies have denounced. There can be no equivalency.
Taking Mosul Aleppo-style would provoke international condemnation and threaten to crack the U.S.-led coalition. A wholesale slaughter would also guarantee the enduring hostility of Iraq’s Sunni population.
A city that initially fell to ISIS in less than a week in 2014 will take a much longer time to recapture, but neither Washington nor Baghdad will want to see the battle of Mosul become a protracted siege, which may dishearten the attackers, try American patience and increase pressure for escalation to finish the brawl.
Protracted battles also increase the risks of terrible mistakes — ISIS defenders will try to lure attackers into accidentally killing civilians. A long battle also increases the risks of the occurrence of external events, such as political upheavals elsewhere, new crises or major terrorist attacks, that can fundamentally alter strategic calculations in Iraq.
The battle of Mosul is not just about defeating ISIS. It is about restoring Mosul to the multi-ethnic city it once was, which is a microcosm in recreating Iraq as a diverse but unified, multi-ethnic, multi-sectarian state.
The United States portrays the battle of Mosul as one of liberating the city from its brutal ISIS occupiers. It is, of course, controversial, but reducing resistance in Mosul by allowing some desperate fighters to flee — enabling the Iraqi forces to achieve an easier morale-building victory — may be strategically and politically preferable to a long and savage battle to retake the city street by street.
What happens after the fighting will be as important as the battle itself, and may be even more difficult.
The United States, and presumably the government of Iraq, will want to avoid the reprisals that have marred some of Iraq's previous "liberations" of towns held by ISIS. That means maintaining discipline in the Iraqi army and holding the Shiite militias in check.
Shiite volunteer units, motivated by religious sentiments and historic grievances, have been ardent and ferocious fighters against the Sunnis in ISIS, but they also have exhibited a tendency to settle scores with summary executions and property seizures. The heavy casualties that come with urban warfare — especially snipers and booby traps that impose casualties without a visible enemy to shoot back at — make it more difficult to keep bloodlust under control.
From the perspective of reconciliation, the United States may choose to treat Mosul's civilian inhabitants as victims of occupation rather than as ISIS collaborators, even while knowing that this is not entirely true. Some ISIS fighters, no doubt, will try to escape with the refugees; all young men will be suspect.
Some may be diehard followers of al-Baghdadi. Others may justifiably claim that they were coerced into service or that economic survival gave them no choice but to draw pay as ISIS soldiers.
Beyond the fighters, however, are those who will have been active collaborators.
The issue in dealing with them is not justice, but the concern that as ISIS goes underground, they will be ISIS's spies and enablers.
The local population knows who they are, but may be reluctant to point them out for fear of future reprisal or conviction that a Sunni underground may be their only insurance policy against Shiite retribution. False accusations can also be expected as the unfortunate citizens of Mosul curry favor among the new occupiers and/or settle their own scores.
Distinguishing a future terrorist underground from the merely unfortunate will require segregation and interrogation while not allowing intelligence operations to turn into opportunities for wreaking vengeance. This is not something U.S. personnel will have the mandate or skills to do.
Captivity for some fleeing from or freed in Mosul could also create tensions with the United Nations and international aid organizations, which may tend to see those streaming out of or left behind in Mosul from strictly a humanitarian point of view. Large-scale imprisonment will not necessarily work either, unless accompanied by effective de-radicalization and rehabilitation.
One must remember that ISIL itself was nurtured in a U.S.-run prison in Iraq.
The battle of Aleppo is now in its fifth year. Syrian government forces control the western half of the city while a coalition of rebel forces, including both jihadist and secular formations supported by the West, occupy its eastern half. The rebel forces — whose numbers may range from 8,000 to 15,000 fighters — confront Russian-supported Syrian government forces, pro-government militias and Shiite "volunteer" units from Iran, Iraq and Lebanon, including Hezbollah.
Before the outset of Syria's civil war, Aleppo's population exceeded 2 million people, making it Syria's most populous city and roughly the same size as Mosul before its capture by ISIS. Approximately 80 percent of the inhabitants were Sunnis, making Aleppo a hotbed of resistance, although not all Sunnis opposed the regime, and even fewer took up arms.
Today, about 275,000 civilians are believed to still reside in the eastern, rebel-held part of the city, while an estimated 1.5 million live in the government-controlled western part.
The current government offensive in Aleppo began in June. By late July, government forces had succeeded in cutting off the last rebel corridor between Aleppo and the Turkish border. Efforts to drive the rebels out of Aleppo escalated in September. The battle has been characterized by artillery barrages and heavy bombing by Russian and Syrian aircraft, including Syria's continuing use of "barrel bombs," improvised but highly destructive devices responsible for thousands of deaths. The United Nations has denounced their use.
The government's tactics appear deliberately indiscriminate. The U.N.'s human rights chief has described them as war crimes. Where targeting is apparent, it appears to be aimed at schools, hospitals and rescue workers.
This kind of warfare reflects Syria's and Russia's approach to counterinsurgency, which aims at making life untenable in zones outside of government control by attacking commerce, food production, public health and other essential services necessary for day-to-day living.
It makes no distinction between rebel fighters and noncombatants.
Such tactics, plus indiscriminate attacks and atrocities by jihadist fanatics like ISIS, which advertises unlimited violence and atrocities as evidence of its authenticity, have turned more than half of Syria's pre-war population into refugees seeking safety inside and outside Syria.
The Syrian government seems determined not just to annihilate the rebels in Aleppo, but to depopulate the rebel-held part of the city.
Syria's ruthless strategy in the battle of Aleppo recalls both Syria's own history and that of the Soviet Union in dealing with internal threats. In response to a Sunni Muslim Brotherhood uprising in 1982, Hafez Assad — then-president of Syria and father of current President Bashar Assad — shelled the rebels' stronghold in the city of Hama, killing tens of thousands in order to root out a few hundred insurgents.
It was deliberately brutal and broke the back of the rebellion. Syrians are still haunted by the event.
From the 1930s into the 1950s, Soviet dictator Joseph Stalin forcibly transferred entire populations: masses of people considered a potential security threat on the basis of class or ethnic identity. It is estimated that these forced internal migrations affected as many as 6 million people.
Millions died on the way to or during their harsh exile in Siberia, but the internal deportations snuffed out actual, imagined and potential opposition to the regime. Some, like the survivors of the hundreds of thousands of thousands of Chechens deported in the 1940s, were not allowed to return to their homes until the 1990s.
What is taking place in Aleppo is not senseless violence, from the Syrian regime's perspective. It denies rebels popular support, not by winning hearts and minds or turning the population against the rebels, but rather by turning the people into refugees on the run or reducing them to subsistence-level.
It is a means of creating terror and thereby a warning to other Syrian towns that even the presence of rebels will bring total destruction. It also radicalizes the surviving rebels, propelling them into the ranks of the fanatics whom many Syrians and foreign powers regard with equal or greater dread.
The Assad regime emerges as the lesser of two evils.
Syrian authorities have little concern about identifying who among the civilians might secretly support the rebels. A civilian in a rebel-held zone, by geographic definition, is a rebel supporter, whether out of sympathy or as a consequence of coercion.
But the slaughter currently taking place in Aleppo also betrays the Syrian government's vision of what Syria will be in the future.
It makes reconciliation between its minority Alawite-dominated regime and its Sunni majority population impossible. The conflict has become existential for all sides. Syria is effectively partitioned along sectarian and ethnic fault lines.
The government's style of warfare deepens rather than bridges these divisions. It accepts that Syria will remain a divided country with a government controlled enclave connecting Damascus, Aleppo, and the Western governorates, separate Kurdish enclaves in the north, which are a great concern for Turkey, and a vast ungoverned Sunni badlands to the east, much of which is still dominated by ISIS.
Perhaps, when world attention turns to other matters, this part of Syria can gradually be reconquered, but for the immediate future, it is a terrorist problem for the West. In the context of this vision of the future, the battle of Aleppo is nothing more than sectarian and political cleansing.
The Syrian government's strategy undermines any American illusions about the prospects for a grand negotiated settlement for the country that will bring peace and eventually produce a democratic government of national reconciliation that is able to command the allegiance of all its people. The difficulty of even a partial cessation of hostilities in Syria was underscored by the failure of the recent cease-fire negotiated by Russia and the United States, which took months to put into place.
Syrian strategy — brutal and meriting international condemnation as a war crime — in the short run may prove more effective than Western efforts, which rest upon being able to make fine distinctions among Syria's myriad of rebel factions and turn the more acceptable groups into an effective force capable of resisting the government's onslaught while simultaneously destroying dangerous jihadists to protect the West and other countries against their terrorist campaigns.
Both Syria and Russia disregard world opinion. Bashar Assad is desperate and has nothing to lose. Russian President Vladimir Putin's attitude is one of disdain, based upon a calculation that there is little support among Russia's accusers for confrontation over the plight of Syria's rebels or its unfortunate civilians. That makes things easier for Damascus and Moscow.
Aleppo is the result. Mosul poses a more difficult challenge.
Jenkins is a senior adviser to the president of the nonprofit, nonpartisan RAND Corporation, and the author of the recent RAND report "How the Current Conflicts Are Shaping the Future of Syria and Iraq."
The views expressed by contributors are their own and not the views of The Hill.