Revolt of the Three Feudatories
After suppressing the Revolt of the Three Feudatories and the conquest of Taiwan as well as ending the Sino-Russian border conflicts in the 1680s, the Dzungar–Qing War broken out. This eventually led to Qing conquests of Outer Mongolia, Tibet, Qinghai and Xinjiang. All of them became part of the Qing Empire and were garrisoned by Qing forces, but they were governed through several different types of administrative structures and also retained many of their existing institutions. Furthermore, they were not governed as regular provinces (until Xinjiang and Manchuria were turned into provinces in late Qing), but instead were supervised by the Lifan Yuan, a Qing government agency that oversaw the empire's frontier regions.