Given the clampdown on foreign fighters and the changed environment in Syria and Iraq, the group may be unable to break out as broadly as it once did, so Washington's approach should shift accordingly.
When the Islamic State was pushed out of Mosul and Raqqa, many analysts noted that it would not represent a complete defeat for the group, but rather a return to a different level of insurgency. Such arguments also implied that IS may take advantage of future cleavages and vacuums in Iraq and Syria just as it previously did in 2009-2012, the interregnum between its tactical defeat as "the Islamic State of Iraq" and its reemergence in April 2013. What led to this reemergence, and how does the current environment compare to that of the group's first "defeat"? Answering these questions can shed light on the trajectory of any future IS comebacks and the related debate about the future of U.S. troops in Iraq and Syria.
HOW DID THE GROUP REMAIN AND EXPAND?
Five main factors allowed IS to reemerge in 2013: the U.S. withdrawal from Iraq in December 2011 and the corollary weakness of the Iraqi security forces; the group's continued participation in local criminal enterprise; the group's ability to exploit Iraqi Sunni grievances against the Shia-majority central government; mass prison breaks by IS comrades in Iraq; and the outbreak of the Syria war, which spurred an unprecedented mobilization of foreign fighters.
U.S. withdrawal, Iraqi security weaknesses. It is no surprise that new opportunities arose for IS due to the massive disparity between Iraqi and American security capabilities. If Iraq's military and intelligence apparatus had been strong enough, the U.S. departure would not have mattered as much. Instead, the withdrawal gave IS members greater freedom of movement and operation in areas where they had previously established a strong presence or extensive support networks, which U.S. forces had been careful to suppress over the course of the surge and Sunni "Awakening" movement.
Criminal enterprise. The post-2011 vacuum gave IS more opportunities to exploit or create criminal networks engaged in human trafficking, kidnapping, extortion, bank looting, rudimentary oil refining, and antiquities trafficking. The group also made undercover investments in legitimate local businesses to build up its monetary assets.
Sunni grievances. In the wake of the U.S. withdrawal and Awakening movement, Iraqi prime minister Nouri al-Maliki promised to integrate the political system and security services with those Sunnis who had helped fight IS in parts of Anbar province between 2006 and 2009. Over time, however, he grew more and more paranoid over the possibility that minority Sunnis might return to power and install another tyrant along the lines of Saddam Hussein. Such fears led the government to marginalize Sunni actors, spurring a protest movement in December 2012. When the government destroyed a protest camp in Ramadi a year later, it helped reignite a broader insurgency that IS was well placed to exploit.
Prison breaks. From 2011 onward, high-profile prison breaks in Abu Ghraib, Taji, and elsewhere allowed key IS operatives and leaders who had been arrested during the surge/Awakening years to return to the group. Many of these escapees were skilled, battle-hardened fighters who served as potent force multipliers and recruiters.
The Syrian jihad. Perhaps more than any other factor, the Syria war gave IS unparalleled access to new recruits, weapons, and funding. This included a large flow of foreign fighters willing to help it win battles and administer areas under its control. Although this mobilization was driven by many factors, Turkey's strategic location in the region and its open border with Syria were perhaps the most important enablers—the flow of fighters over this frontier went unimpeded until sometime around spring 2015, when Ankara began to take the issue more seriously.
SIMILARITIES AND DIFFERENCES TODAY
In its current incarnation, IS continues to exploit criminal enterprises, Sunni grievances in Iraq, and the Syria war, but other factors have emerged that will likely blunt its prospects of rebounding quite as triumphantly as it did in 2013-2014. If and when IS reclaims territory, it will probably be more akin to an archipelago of strongholds than the large swaths of land it once took so rapidly.
One reason behind this limitation is that the region is highly unlikely to see a repeat of the massive foreign fighter mobilization that occurred in 2012-2015. Although jihadists will continue trying to infiltrate Iraq and Syria, their numbers should be more of a trickle than a torrent given the new legal regimes that various governments have implemented against such recruitment and Turkey's continued crackdown on foreign fighter movement through its territory. Therefore, IS will have much less potential manpower to help rebuild its governance architecture or serve as cannon fodder.
Moreover, the Popular Mobilization Forces (PMF) in Iraq and the constellation of local and foreign Shia militias in Syria will not tolerate a massive IS rebuilding effort, especially those aligned with Iran. Since the liberation of Mosul, some PMF militia units have already overcompensated on that front, not only suppressing IS-related activity but also taking action against unassociated Sunni communities. Ironically, such actions will likely create a base for future IS recruitment, especially since the Sunni community has been left with few local leadership alternatives following a half-decade of IS campaigns against former Awakening figures and other Sunni political and insurgent actors. Yet growing Iranian influence and greater discipline among the PMF mean that any new IS breakout would probably involve far smaller pockets of territory and generate a rapid military response, making any gains more difficult to sustain or broaden. One potential wildcard is the re-creation of al-Qaeda's network in Iraq, but while this idea has been rumored within jihadi circles for a couple years, it has yet to come to fruition.
Lastly, the ground next door in Syria is not as fertile for jihadist takeover as it used to be. The Assad regime and the Kurdish-led Syrian Democratic Forces continue to win territory, and the Sunni Islamist groups that gave space to IS between April 2013 and January 2014 (including Jabhat al-Nusra, al-Qaeda's branch at the time) would not do so again. In fact, the Sunni backlash against IS in Syria has been even firmer than that seen in Iraq after the Awakening movement. In short, IS would have far more difficulty harnessing Syrian Sunni actors for its own gain today than it did before it conquered Raqqa and other parts of the country in 2014.
Given these factors, the scenario that played out between December 2011 and June 2014 is unlikely to be repeated, at least not in the same scope or pace. Although some of the conditions and underlying structural problems that led to the group's reemergence remain intact, crucial differences need to be taken into account as well. Of course, it would be foolish to count IS out—for one thing, the group is stronger now than it was following its first "defeat" in 2009. Yet the international clampdown on foreign fighters, the greater vigilance seen among local enemies of IS, and the changed environment in Iraq and Syria all indicate that the group may be unable to assert itself as broadly or quickly as it did in 2014.
Washington and its allies should therefore focus on fully understanding this changed context, not on refighting the previous battle. Strengthening Iraq's security forces would be a particularly beneficial first step, both to avoid repeating past failures and to limit the role that Iranian-backed militias play in Iraq's future. Such an approach would also alleviate the burden on U.S. forces, which could then focus more on figuring out how to influence events on the ground in Syria despite the lack of U.S. relations with the Assad regime. In the longer term, there is no quick remedy to the IS threat in either country. Even so, the United States should work with local and international partners on the crucial task of resolving the underlying political, economic, social, environmental, and religious problems that IS and other jihadi groups capitalize on.
Aaron Y. Zelin is the Richard Borow Fellow at The Washington Institute.