In the messy patchwork of conflicts raging across the Middle East, one country has been absent from the spotlight: Syria.

A civil war that dominated international headlines for more than a decade has now been reignited after a coalition of Syrian rebels launched a lightning offensive last week, seizing Aleppo, the country’s second-largest city, from President Bashar al-Assad’s regime.

The rebels took only hours to recapture territory that Assad’s forces had spent years reclaiming….