Several of the oasis states had once been vassals of the Tang Dynasty, but switched their allegiance to the Western Turks when they grew suspicious of the military ambitions of the Tang.
Beberapa negara oasis pernah menjadi vasal Dinasti Tang, namun mengalihkan kesetiaannya kepada Turk Barat ketika mereka menjadi curiga terhadap ambisi militer Tang.