Less than two years since the beginning of the uprising in Syria, localized protests have morphed into full-blown civil conflict. What began as youths scrawling anti-regime graffiti in Daraa has given way to a countrywide insurgency that pits regime loyalists against a hodgepodge of army defectors, volunteers, and committed jihadists. Parallel to this internal escalation, the conflict has drawn in external actors, including both Syria’s neighbors and extra-regional powers. There is a cruel irony in Syria emerging as an arena of strategic competition: The country that has traditionally used neighboring states as terrain for prosecuting its own conflicts has now...