The Islamic State of Iraq and al-Sham (ISIS), which is also called the Islamic State, is on the march. Two months after first sweeping through northern and central Iraq, it has started to push onward to Erbil, the seat of the Kurdish Regional Government. Along the way, it triggered a severe humanitarian crisis among Iraq’s Yezidi and Christian minorities and caused massive panic across the Kurdish autonomous region, which forced a reluctant United States to intervene. ISIS has also used its momentum to continue its expansion in Syria and, for a few days, even managed to hold parts of the Lebanese border city of Arsal. More confident than ever, ISIS is taking on a broad array of enemies, including the Iraqi, Syrian, and Lebanese militaries; Iraqi and Lebanese Shia militias; Kurds from Iraq, Syria, and Turkey; and Islamist and secular Syrian opposition forces. Now even U.S. air power is joining the fray.

From a military perspective, ISIS’ willingness to fight so many groups on so many fronts is impressive. In part, its boldness was made possible by the weakness of many of its rivals. The huge store of deadly, high-quality weapons that the group picked up on its march through Iraq has helped as well. Finally, ISIS has also demonstrated a surprising ability to rearrange and redeploy forces as the group’s operational needs change. Its reputation for military prowess (and brutality) has only grown, which in turn has further weakened resistance to its moves and sent civilians running whenever ISIS forces got close.

ISIS’ relatively unimpeded march toward Erbil caught the White House and many other observers by surprise. Most had expected that the jihadist group would concentrate its efforts in Iraq on Baghdad, the capital and a historical seat of the Abbasid Caliphate, where numerous Sunni reside. They also believed that the Kurdish peshmarga forces were strong enough to deter ISIS attacks and would be able to block its advance if deterrence failed. That turns out to have been wrong, a miscalculation that forced the Obama administration’s hand. Still, because ISIS’ move provoked a U.S. bombardment, some believe it might well be its undoing.

For that reason, ISIS’ strategy might seem like a surprising overreach. It is entirely consistent, however, with the path the group charted early on, which tended toward the bold and risky. In fact, ISIS’ recent moves are simply a continuation of prior efforts to expand its control over new territory and natural resources (primarily oil fields and water dams that it can use for income and tools of war), enforce its harsh ideology, and strengthen its own primacy within the jihadi camp.

For now, it is impossible to say whether ISIS intended to provoke the United States to intervene or simply miscalculated. But it is hard to believe ISIS did not understand that threatening the capital of Iraqi Kurdistan would mean directly challenging the U.S. alliance with the Kurds and potentially provoking it to fight. Indeed, it is likely that ISIS viewed such a challenge as a win-win situation.

If the United States had failed to protect its allies, ISIS forces would have been able to advance deep into Kurdish territory and masses of “undesirable” non-Sunni inhabitants would have fled. The demonstration of U.S. timidity would also have given ISIS a boost as it set its sights on Jordan, another anxious U.S. ally in need of Washington’s defense.

If the United States decided to step in on behalf of its allies -- as it did -- then ISIS must have believed that it would be able to strengthen its position within the jihadi camp. ISIS could use the bombings as evidence that the United States is waging a war on Islam, and to portray itself as the defender of Muslims from “Crusader” aggression. In other words, ISIS would steal a page right out of al Qaeda’s playbook. And that puts more pressure on al Qaeda. After all, if ISIS wins vast territory in the heart of the Middle East, implements Islamic governance, and battles apostate regimes and their backers, al Qaeda will -- after refusing to do so -- have to give its full support to ISIS. Already, ISIS supporters are calling all jihadi forces to stand behind Omar al-Baghdadi, the leader of ISIS. As a result, the flow of fighters abandoning al Qaeda affiliates to join ISIS, which U.S. intelligence has already observed, is likely to increase. Moreover, leaders of al Qaeda franchises will come under greater pressure to shift allegiance from al Qaeda to ISIS.

Of course, getting the United States involved carries considerable risks. ISIS does not have an answer to American airpower. From the air, the United States is capable of delivering painful blows that can significantly degrade the group. And by supporting Kurdish forces on the ground, U.S. intervention could even reverse ISIS’ advances in the north. But U.S. President Barack Obama’s caution when it comes to foreign interventions, and his obvious distaste for getting entangled in Iraq again, appear to have mitigated the risks for ISIS. Indeed, the United States seems intent on the most minimal intervention possible, striking very few targets, and aiming to create deterrence more than rolling back ISIS advances on the ground. Moreover, Obama’s aversion to doing anything in Syria means that ISIS-controlled territories there will be a safe haven for the group no matter what happens in Iraq.

Although the push against the Kurds can be seen as serving the Islamic State’s strategic objectives, the persecution of minorities, particularly the beginning of a genocidal drive against the Yezidis, should be viewed not only as an effort to intimidate the opponents of ISIS, but also as the fulfillment of ISIS’ radical ideology, which includes special taxes for minorities, forced deportations or, as in the case of the Yezidis, a choice between conversion or death. This ideology is an integral part of ISIS’ broader effort to implement Islamic governance and has some precedents in its actions in Syria. In the absence of  concerted international action, it will continue to oppress, chase away, and, in the worst cases, kill minorities under its rule.

ISIS has been clear about its expansionist and exclusionary Caliphate project, and now that truth has finally sunk in with the Obama administration. Getting involved in Iraq carries risks, but if the United States will not lead -- and from the front this time -- the ISIS threat will only grow. A lasting solution to the problem requires deep political changes in Iraq and, just as important, in Syria, which Washington has largely ignored. Such changes are unlikely to materialize fast enough to answer an urgent threat. In the meantime, although a comprehensive aerial campaign could weaken ISIS considerably, the narrow scope of U.S. strikes will provide only modest and insufficient relief. Fighting ISIS will inevitably generate some resentment against the United States. However, the danger that would result from allowing ISIS to expand unchecked is far worse. Unless the United States is willing to walk away from the Middle East for good, it will have to face ISIS head on. And doing so will cost much more the longer the United States waits.  

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  • BARAK MENDELSOHN is an Associate Professor of political science at Haverford College and a Research Fellow at Harvard Kennedy School's Belfer Center for Science and International Affairs. Follow him on Twitter @BarakMendelsohn.
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