The Islamic State of Iraq and Syria has been dominating headlines for the past year and more. But what manner of organization is it? Is it a terrorist group, a guerrilla group, or something else? The answers to those questions, rooted in the study of military history, may hold the key to defeating the evil that is ISIS.
To begin with, although ISIS is commonly branded a terrorist organization, it is far larger than most previous terrorist groups. Organizations such as the Russian Nihilists, the German Baader-Meinhof Gang, the Provisional IRA, and al-Qaeda have typically deployed a few hundred fighters at most, and they have not been able to control terrain. ISIS, by contrast, has more than 20,000 fighters, many of them armed with Humvees, tanks, and other heavy equipment captured from the Iraqi army, and it controls territory in Iraq and Syria equivalent in size to the United Kingdom.
ISIS, in short, is in the process of making a very unusual transition, going from a terrorist organization to a state of sorts with a burgeoning conventional army. While some guerrilla groups have made this transformation in the past—the Red Army of Mao Zedong and the Vietminh of Ho Chi Minh are prime examples—only one other terrorist organization has so far pulled off this feat.
That would be Hezbollah, which is in many ways ISIS’s mirror image—an extremist Shiite group that began by carrying out suicide bombings in Lebanon in the early 1980s and now exerts control over the entire Lebanese state and fields its own army equipped with more than 50,000 rockets and missiles. Hezbollah pulled off this accomplishment with considerable support from Iran; indeed it is a virtual adjunct of Iran’s Quds Force. ISIS is, in many ways, even more impressive (or dismaying) for having attained its success without any serious state sponsorship.
What this means is that low-level counter-terrorist operations, consisting of dropping bombs on a few selected leaders, will not succeed in defeating ISIS, any more than Israel succeed in defeating Hezbollah by killing its previous secretary-general in 1992. ISIS has grown strong enough that it will need to be defeated by a conventional offensive, whether by the U.S. military or by American allies in the region. The good news: As Graeme Wood has argued in The Atlantic1 because so much of ISIS’s legitimacy depends on controlling its self-proclaimed caliphate, the loss of territorial control would be far more devastating to ISIS than it would be for a smaller, less ambitious terrorist organization.
 1 Graeme Wood, “What ISIS Really Wants,” The Atlantic (March, 2015). http://www.theatlantic.com/features/archive/2015/02/what-isis-really-wants/384980/