What’s happening in Syria? How an old conflict in the Middle East erupted again

The rebels took only hours to recapture territory that Assad’s forces had spent years reclaiming. Fighter jets from Syria and its ally Russia soon began bombing the area — killing hundreds of the rebels but civilians, too, according to a leading monitoring group. “This is a very unstable situation with a huge amount of flux,” said H.A. Hellyer, a senior associate fellow at the Royal United Services Institute, a London-based think tank.