Hans Bielenstein writes that as far back as the Han dynasty (202 BCE–220 CE), the Han Chinese government "maintained the fiction" that the foreign officials administering the various "Dependent States" and oasis city-states of the Western Regions (composed of the Tarim Basin and oasis of Turpan) were true Han representatives due to the Han government's conferral of Chinese seals and seal cords to them.
What was the western regions composed of?
the Tarim Basin and oasis of Turpan