In 2013, Assad used chemical weapons against rebel groups several times. After more than a thousand civilians were killed in one case, the Obama administration declared that Syrian President Bashar Assad had crossed a red line. Washington threatened to attack in response but backtracked after reaching an agreement with Russia to dismantle Assad’s stores of chemical arms.
By early 2014, the weapons caches had been removed from Syria, and Western intelligence agencies believed that the Assad regime retained just a small amount of chemical arms for use if Assad’s rule were directly threatened. On a number of occasions, the regime used less-lethal chemical weapons like chlorine bombs.