Why Idlib matters and the obstacles Assad faces there

The Syrian conflict has turned toward the northwestern Idlib region, where government preparations for a Russian-backed offensive have sparked a concerted Turkish diplomatic bid to prevent an attack.A major assault in Idlib, home to some three million people, could be more deadly and destructive than any other in a war that has killed hundreds of thousands of people since 2011.The U.N. is warning of a humanitarian catastrophe.