For decades, the Syrian strongman Bashar al-Assad built his power on a single, relentless narrative of survival: The regime presented itself as the only shield against annihilation for the Alawites, the ethno-religious minority that makes up about a tenth of Syria’s population and has long understood itself to be threatened by the country’s Sunni majority.Supporting Assad, himself an Alawite, was a matter not of loyalty or politics for this community, the regime insisted, but of choosing between existence and extinction. This narrative, and the fear of Sunni extremist groups such…