Basically the CIA helped flood the region with Salafist texts and ideology in the leadup to fomenting the soviet afghan war, which was actually just the soviets supporting the social democrat elected government of Afghanistan at the time which the CIA helped to overthrow. This reactionary propaganda did not contain itself in the borders of Afghanistan but spilled over into neighboring regions such as western China. Fast forward a couple decades and those same proto-ISIS aligned groups go on to commit a series of bombings and attacks in west china resulting in a state crackdown and reeducation effor. Preserving the Uyghur culture while stamping out the Salafist influences imported from the west.

That's the bare bones of it.

There was terrorism committed by Muslim extremists supported by the US. China's policy has been to educate and integrate uyghurs into Chinese society.