The U.S left supplies, vehicles, amunition and weapons on the ground when they pulled out instead of destroying everything as is the basic rule when retreating - it all seems a little suss to me.
Add to that the air drops that conveniently ended up in the hands of ISIS instead of the Kurds and it doesn't take a genius to question what their intentions really were. The famous photos of ISIS huge convoy of brand spanking SUV's snaking down the roads makes one question why they were never targetted by drones or aircraft at the time either

The U.S has used these tactics time and time again, funding the likes of Al Qaida and the rebels in Libya to oust Gaddafi, just to name a few in modern times... not to mention the countless cock ups in central and south America..