The situation in the north, in the state of Wei (220-265) was anything but rosy. Wei ruled what at that time were the most important and richest regions of China, the plain of Shensi in the west and the great plain east of Loyang, the two most thickly populated areas of China. But the events at the end of the Han period had inflicted great economic injury on the country. The southern and south-western parts of the Han empire had been lost, and though parts of Central Asia still gave allegiance to Wei, these, as in the past, were economically more of a burden than an asset, because they called for incessant expenditure. At least the trade caravans were able to travel undisturbed from and to China through Turkestan. Moreover, the Wei kingdom, although much smaller than the empire of the Han, maintained a completely staffed court at great expense, because the rulers, claiming to rule the whole of China, felt bound to display more magnificence than the rulers of the southern dynasties. They had also to reward the nineteen tribes of the Hsiung-nu in the north for their military aid, not only with cessions of land but with payments of money. Finally, they would not disarm but maintained great armies for the continual fighting against the southern states. The Wei dynasty did not succeed, however, in closely subordinating the various army commanders to the central government. Thus the commanders, in collusion with groups of the gentry, were able to enrich themselves and to secure regional power. The inadequate strength of the central government of Wei was further undermined by the rivalries among the dominant gentry. The imperial family (Ts'ao Pei, who reigned from 220 to 226, had taken as emperor the name of Wen Ti) was descended from one of the groups of great landowners that had formed in the later Han period. The nucleus of that group was a family named Ts'ui, of which there is mention from the Han period onward and which maintained its power down to the tenth century; but it remained in the background and at first held entirely aloof from direct intervention in high policy. Another family belonging to this group was the Hsia-hou family which was closely united to the family of Wen Ti by adoption; and very soon there was also the Ssu-ma family. Quite naturally Wen Ti, as soon as he came into power, made provision for the members of these powerful families, for only thanks to their support had he been able to ascend the throne and to maintain his hold on the throne. Thus we find many members of the Hsia-hou and Ssu-ma families in government positions. The Ssu-ma family especially showed great activity, and at the end of Wen Ti's reign their power had so grown that a certain Ssu-ma I was in control of the government, while the new emperor Ming Ti (227-233) was completely powerless. This virtually sealed the fate of the Wei dynasty, so far as the dynastic family was concerned. The next emperor was installed and deposed by the Ssu-ma family; dissensions arose within the ruling family, leading to members of the family assassinating one another. In 264 a member of the Ssu-ma family declared himself king; when he died and was succeeded by his son Ssu-ma Yen, the latter, in 265, staged a formal act of renunciation of the throne of the Wei dynasty and made himself the first ruler of the new Chin dynasty. There is nothing to gain by detailing all the intrigues that led up to this event: they all took place in the immediate environment of the court and in no way affected the people, except that every item of expenditure, including all the bribery, had to come out of the taxes paid by the people.

With such a situation at court, with the bad economic situation in the country, and with the continual fighting against the two southern states, there could be no question of any far-reaching foreign policy. Parts of eastern Turkestan still showed some measure of allegiance to Wei, but only because at the time it had no stronger opponent. The Hsiung-nu beyond the frontier were suffering from a period of depression which was at the same time a period of reconstruction. They were beginning slowly to form together with Mongol elements a new unit, the Juan-juan, but at this time were still politically inactive. The nineteen tribes within north China held more and more closely together as militarily organized nomads, but did not yet represent a military power and remained loyal to the Wei. The only important element of trouble seems to have been furnished by the Hsien-pi tribes, who had joined with Wu-huan tribes and apparently also with vestiges of the Hsiung-nu in eastern Mongolia, and who made numerous raids over the frontier into the Wei empire. The state of Yen, in southern Manchuria, had already been destroyed by Wei in 238 thanks to Wei's good relations with Japan. Loose diplomatic relations were maintained with Japan in the period that followed; in that period many elements of Chinese civilization found their way into Japan and there, together with settlers from many parts of China, helped to transform the culture of ancient Japan.