Final answer:
The late Tang dynasty employed Uighurs as military forces to maintain their empire, which faced decline due to various defeats and internal revolts.
Step-by-step explanation:
During the late period of the Tang dynasty, internal and external challenges led to a reliance on foreign military assistance. Notably, the Tang government employed the Uighurs, a Turkish-speaking people from the northwest region, as part of their military forces.
This was not unusual for the Tang, as they incorporated international talent within their ranks, including those from Koguryo and Sogdian backgrounds, to maintain their expansive empire covering over four million square miles of territory.
The Tang dynasty eventually faced decline due to defeats like the one at the Battle of Talas River and internal revolts. After the disintegration of the Tang dynasty in 907 CE, the power vacuum led to the rise of other entities like the Khitan Liao and the Xi Xia kingdoms, formed by steppe peoples such as the Khitan and the Tanguts.
The Uighurs eventually allied with the Tang to defeat the rebellion led by General An Lushan in 755.
In more recent times, the Uighurs have been seeking independence due to increasing sinicization policies in the Xinjiang region. Instances of unrest and conflict have occurred, such as the July 2009 clashes that resulted in significant loss of life.
Reports have also emerged about Uighurs from Xinjiang joining extremist groups and the Chinese government's efforts to assimilate Uighurs through controversial 're-education centers'.