Due to the decline of Tang central authority after the An Lushan Rebellion (755–763), there was growing tendency to superimpose large regional administrations over the old districts and prefectures that had been used since the Qin dynasty (221–206 BC). These administrations, known as circuit commissions, would become the boundaries of the later Southern regimes; many circuit commissioners became the emperors or kings of these states. The administrations of the Five Dynasties and the early Song dynasty shared a pattern of being disproportionately drawn from the families of military governors in northern and northwestern China (Hebei, Shanxi, Shaanxi), their personal staff, and the bureaucrats who served in the capitals of the Five dynasties. These families had risen to prominence due to the unraveling of central authority after the An Lushan Rebellion, despite lacking esteemed ancestry. The historian Deng Xiaonan argued that many of these military families, including the Song imperial family, were of mixed Han Chinese-Turkic-Kumo Xi ancestry. Even the rulers of the Southern states were almost all military leaders from the north with their key officers and elite forces also hailing from the north, since the bulk of the Tang army was based in the north.