US and Turkey force Kurds to hand back strategic Syrian city to ISIS?Watch
There is two reasons:
1) Turkey doesn't want a free Kurdistan in Syria and the US wants to keep Turkey and Erdogan happy.
2) The US who want rid of Assad see that the Kurds as having a negative impact on Daesh in their war against Assad. If the Kurds are forced to retreat that will allow Daesh supply routes to reopen and allow Daesh to launch further attacks on Assads forces. It's speculated that Damascus could fall to the FSA or Daesh by October with Assad forced to flee Syria.
This is tragic news. When Manbij was liberated its people were so happy and grateful that their ordeal was over. Kurds showed the torture centres use by Daesh and their gruesome killing methods. Now the people of Manbij are now forced to endure the return of Daesh. That's the US and Turkey for you!
I'd sooner Britain left NATO and joined with Russia instead if that's how the west treats people like the Kurds.