Rebel Coalitions' Strength Rivals That of the Islamic State

Islamic State fighters are reportedly positioning their forces around Deir el-Zour's military airport, highlighting the possibility that the air base will be the group's next target.

The Islamic State has faced some setbacks in Iraq after stiffening resistance from the Iraqi army and peshmerga forces supported by U.S. air power. But as the Aug. 24 seizure of the Tabqa airbase proved, the Islamic State continues to be a lethal threat in Iraq and Syria. Islamic State fighters are also extremely determined, continuing to pursue their objectives even while sustaining very heavy casualties. Furthermore, they are mobile, disciplined and adept at small-unit tactics.