Military Implications of the Syrian Regime's Defeat in Raqqa
"The most effective way to stop ISIS and then roll it back would be a combined effort involving well-armed and supported Syrian rebel forces and U.S./allied airpower, all working under a coherent long-term strategy and conducting coordinated operations to defeat the group's forces and free areas under its control. Failing that, more limited measures -- such as arming the rebels and using airpower to reduce ISIS forces and capabilities -- would be useful in preventing more dramatic gains in Syria and perhaps rolling back the group's recent progress in northern Aleppo."