Over the course of the US involvement in Syria, the relative lack of allies has repeatedly been approached the same way by the Pentagon: try to make some. The US has repeatedly bankrolled very expensive endeavors in Turkey trying to form brand new Syrian rebel factions explicitly made to fight ISIS, and those plans repeatedly collapsed in
Pentagon Creating Yet Another Syrian Rebel Faction For Raqqa Invasion
The US strategy for the invasion of Raqqa appears to hinge on the idea that the US can manufacture a whole new pro-US force that will get to keep the city after the Kurdish YPG conquers it.