The Massacre Strategy

Over the weekend, dozens of pictures trickled out on one of the official Twitter accounts of the Islamic State of Iraq and al-Sham, the jihadist group currently setting off a panic in vast swathes of northern Iraq. The graphic photographs, according to ISIS, showed mass executions of Shiite soldiers who had fought in the Iraqi government's military and security forces. In the images, ISIS fighters corral hundreds of individuals into trucks, forcing them to lie down in shallow graves with their heads to the ground, and then shooting them with Kalashnikovs.

ISIS claimed it had killed more than 1,700 people, though the pictures account for a few hundred at most. Though shocking, this level of brutality is hardly new for the extremist Sunni group, as it has attempted to provoke the Shiite population going back to last decade, when the volatile Abu Musab al-Zarqawi was its leader.

ISIS subscribes to takfir, a practice according to which it believes it is legitimate to kill a Muslim who has abandoned its hard-line interpretation of Islam. Last decade, when ISIS was under the control of Zarqawi and was then called Al Qaeda in the Land of Two Rivers (better known as Al Qaeda in Iraq, or AQI), it used takfir to justify the murder of not only the Shiite population of Iraq but also other Sunnis who did not follow AQI's narrow and severe interpretation of sharia, or Islamic law. (This broad use of takfir ended up backfiring against AQI, since most Iraqi Sunnis did not want to live under such an oppressive group.)

So ISIS, the latest incarnation of AQI, has religious reasons for massacring Shiites, all of whom it views as apostates. And there's another motivation for it as well: old-fashioned vengeance. As ISIS's official spokesperson noted in an audio message posted June 11, "It is true that between us revenge awaits...a long and heavy revenge awaits. However the revenge shall not be in Samara or Baghdad, but rather it shall be in Karbala the city made filthy, and in Najaf the polytheist city, so wait." (Karbala and Najaf are important Shiite shrine cities.) So in ISIS's estimation, its attacks on Shiites are merely retaliation for the Iraqi government's actions against Sunnis.

But there's also a strategic reason behind the executions -- and the gruesome pictures posted online for all to see. ISIS's goal is not only to scare Iraqi Shiites but to provoke them to radicalize, join Iranian-sponsored militias and then commit similar atrocities against Sunnis. ISIS then hopes to set itself up as the protectors of the Sunni population, helping to consolidate its hold on Sunni population centers.

This strategy turned out badly in the recent past. In 2006 and 2007, AQI bombed Samarra's al-Askari Mosque, a holy shrine for Shiite Muslims. In the aftermath, Shiites launched major retaliatory attacks against the Sunni population, kicking off a civil war that radically changed the makeup of Baghdad's population through anti-Sunni death squads. AQI might have gained some leverage or sympathy with the Sunni population at first, but it overplayed its hand by imposing a harsh rule on much of Anbar province. Sunni tribes rebelled, with U.S. help and encouragement, and pushed out the jihadists.

Some within both the Sunni and Shiite communities hope there isn't a recurrence of widespread sectarian violence. Sunni tribal leaders in Mosul and Ramadi, for example, called to fight against both the government and ISIS. Shiite cleric Grand Ayatollah Ali al-Sistani called upon Shiites to stand up against ISIS, but only within the framework of the Iraqi state apparatus, an implicit slight against Iran and its proxies.

Though Sistani framed his appeal in nationalistic terms, tens of thousands of Shiite volunteers reportedly have responded, and Prime Minister Nuri al-Maliki has shown no sign of tempering his anti-Sunni outlook. On Tuesday, the bodies of 44 Sunni prisoners were dumped in Baquba, a mixed town only a few dozen miles from Baghdad -- suggesting it will be difficult to contain the sectarian fires.

ISIS, moreover, is far better organized -- and, with its seizure of oil fields in Syria and banks in Iraq, better financed -- than the AQI of old. The regional context is indeed different, too. American forces are not present to take advantage of a potential second "awakening" movement, and split the tribes from the jihadists. And as we've seen in Syria, although more nationalist and mainstream Islamist groups have pushed ISIS out of certain areas, they haven't been able to strategically cripple them. ISIS's base of operations in Syria also gives the group strategic depth, allowing its fighters to retreat across the border if necessary.

However this plays out in the long run, we will probably be seeing many more pictures of massacred Shiites -- and Sunnis -- before the bloodletting abates.

Aaron Y. Zelin is the Richard Borow Fellow at The Washington Institute and founder of the website Jihadology.net.