With the world now more determined than ever to defeat the Islamic State – an enterprise that will, it is becoming clear, require boots on the ground – the major powers are seeking immediately available forces. For the time being, that means, on the one hand, the Syrian Democratic Forces, dominated by the Kurdish People’s Protection Units, which oppose President Bashar al-Assad’s regime, and, on the other hand, the pro-regime forces backed by Russia, as well as Iran and its proxies, particularly Hezbollah.