The Islamic State is something of an anomaly in Syria鈥檚 civil war, representing a third element in addition to the pro- and anti-Assad forces. Its priority is to carve out and defend an Islamic 鈥渃aliphate鈥 spanning the Syrian and Iraqi borders. Toppling the Assad regime is a secondary consideration. That agenda often places IS at odds with anti-Assad rebel forces, which has led to clashes and feuding over territory.