For years, Turkey has called for a buffer zone in northern Syria, as war devastated the other side of the 900 kilometer border they share. On Wednesday, Ankara made its most significant move so far towards that goal, and Turkey's involvement in the war moved to the next level. Turkish tanks and special forces crossed into Syria, helping a group of rebels to quickly recapture the town of Jarablus from Daesh. But the operation is not just about pushing back Daesh. It's also about ensuring that the power vacuum created isn't filled by the YPG. Yvette McCullough reports on what's being called 'Operation Euphrates Shield'