Domino effect? Assad’s allies stretched thin as Syrian rebels pounce

It took years for Bashar al-Assad’s forces to take back Syria’s second city.

It took days for jihadist-led rebels to overrun Aleppo. Why has a conflict that has been effectively frozen for four years suddenly spring back to life? What to make of Hezbollah, pinned down at home by a precarious truce with Israel, saying it won’t be sending help for now.