The single most important long term development during these centuries was the final re-establishment of Chinese national unity. In the preceding period, the unified empire set up by the Ch’in and the Han had been shattered. The progressive breakdown of central authority in the latter half of the second century was accompanied by the growth of many local power structures. The Yellow Turbans and other popular rebellions of the 180s and the decades of civil conflict and near anarchy which followed them finally destroyed both the effective power and the authority of the Han government. Military force became the sole source of authority, and the emperor became a puppet controlled by the generals. The maintenance of some degree of local stability and law and order lay in the hands of powerful local magnates with personal control over extensive lands and numerous client families of cultivators and military retainers. When the last powerless Han emperor finally abdicated in favor of one of his great generals in AD 220, China was split into three regional states, in none of which did the central government have the unquestioned authority the Han had enjoyed in its prime. Although the whole country was briefly reunited under the Chin in 280, the new regime had little effective power and soon fell victim to serious internal disorders. Almost immediately afterwards, at the beginning of the fourth century, the north was overrun by waves of non-Chinese nomadic peoples, and the Chin survived only as a regional regime in the south. The invaders, the Tibetan Ch’iang and Ti in the northwest, and the Hsiung-nu and various Turkish, proto-Mongol and Tungusic peoples in the north, overran what had been the most advanced, richest and most populous areas of China, establishing a bewildering succession of petty shortlived dynasties. Northern China suffered more than a century of constant warfare, anarchy, disruption and physical devastation before the establishment of a stable unified northern regime by the Toba Turks (the Northern Wei dynasty) in 440.
Although they attempted for decades to preserve their cultural identity, the Toba, like their predecessors, found themselves forced to adopt Chinese institutions and to collaborate with the Chinese elite. Their traditionalist tribal aristocracy, feeling itself about to be absorbed by its Chinese subjects, reacted violently and the ensuing tensions brought about the division of the Northern Wei empire into two states, the Western Wei (which became the Northern Chou in 557) in which the non-Chinese elements remained strongest, and the Eastern Wei (which became the Northern Ch’i in 550) in the northeast. Finally in 577, the Northern Chou conquered the Northern Ch’i, reunifying northern China and reasserting the political and military dominance of the northwest. These centuries of political and social dominance by non-Chinese peoples left deep marks on the society and institutions of northern China. The nobility of the various foreign ruling houses constantly intermarried with the Chinese elite. This was particularly the case in the northwest, where two aristocratic groups emerged to form an elite very different from the traditional Chinese ruling class. These groups, the Tai-pei aristocracy of central and northern Shansi, and the far more powerful Kuan-lung aristocracy with its power bases in southwest Shansi, Shensi, and Kansu, were not only of mixed blood. They had a life style strongly influenced by nomadic customs; even well into the T’ang period many of them still spoke Turkish as well as Chinese; they were essentially a military group rather than a civilian elite, living a hard, active outdoor life; and, as among the nomads, their womenfolk were far more independent and powerful than in traditional Chinese society.
In the northeastern plain, the great aristocratic clans of Shan-tung (the area east of the T’ai-hang ranges, that
