No, arming Syria's rebels wouldn't have stopped ISIS

The idea that these rebel groups could be vetted for moderation and entrusted with advanced weaponry made absolutely no sense given the realities of the conflict in Syria. These local groups frequently shifted sides and formed alliances of convenience as needed. As MIT’s Fotini Christia has documented in cases from Afghanistan to Bosnia, and the University of Virginia’s Jonah Shulhofer-Wohl has detailed in Syria, rebel groups that lack a legitimate and effective over-arching institutional structure almost always display these kinds of rapidly shifting alliances and “blue on blue” violence. A “moderate, vetted opposition” means little when alliances are this fluid and organizational structures so weak.

The murkiness of the “terrorist group” line in this context is apparent in these changing alliances and conflicts. For instance, the United States recently designated two key Kuwaiti Islamists as terror financiers, accusing them of channeling funds to Jubhat al-Nusra and the Islamic State. But both were better known as backers of Ahrar al-Sham, a large Salafist organization that then worked within the Saudi-backed Islamic Front. And as recently as June, when they were allegedly funding the Islamic State and al-Nusra, one of them was holding events with FSA commander Riad al-Assad. These complexities, so deeply familiar to everyone who studies the conflict, deeply undermine the assumptions underlying plans resting on identifying and supporting “moderate rebels.”