The Sui dynasty
The Sui dynasty (581–618), which reunified China after nearly four centuries of political fragmentation during which the north and south had developed in different ways, played a part far more important than its short span would suggest. In the same way that the Qin rulers of the 3rd century bc had unified China after the Zhanguo (Warring States) period, so the Sui brought China together again and set up many institutions that were to be adopted by their successors, the Tang. Like the Qin, however, the Sui overstrained their resources and fell. And also as in the case of the Qin, traditional history has judged the Sui somewhat unfairly, stressing the harshness of the Sui regime and the megalomania of its second emperor and giving too little credit for its many positive achievements.
Wendi (reigned 581–604), the founder of the Sui dynasty, was a high-ranking official at the Bei (Northern) Zhou court, a member of one of the powerful northwestern aristocratic families that had taken service under the successive non-Chinese royal houses in northern China and had intermarried with the families of their foreign masters. In 577 the Bei Zhou had reunified northern China by conquering the rival northeastern dynasty of Bei Qi. However, political life in the northern courts was extremely unstable, and the succession of an apparently deranged and irresponsible young emperor to the Zhou throne in 578/579 set off a train of court intrigues, plots, and murders. Wendi was able to install a child as puppet emperor in 579 and seize the throne for himself two years later.
In control of all of northern China and in command of formidable armies, he immediately set about establishing order within his frontiers. He built himself a grand new capital, Daxing, close to the site of the old Qin and Han capitals, a city erected quickly with a prodigal use of compulsory labour. This great city remained (later under the name Chang’an) the capital of the Sui and Tang dynasties and the principal seat of government until the beginning of the 10th century.
Wendi also took quick action to protect the frontiers of his new state. China during the 6th century had a formidable northern neighbour in the Turks (Tujue), who controlled the steppe from the borders of Manchuria to the frontiers of the Byzantine and Sāsānian empires. At the time of Wendi’s seizure of power, the Turks were splitting into two great empires, an eastern one dominating the Chinese northern frontier from Manchuria to Gansu and a western one stretching in a vast arc north of the Tarim Basin into Central Asia. Wendi encouraged this split by supporting the khan (ruler) of the western Turks, Tardu. Throughout his reign Wendi also pursued a policy of encouraging factional strife among the eastern Turks. At the same time, he strengthened his defenses in the north by repairing the Great Wall. In the northwest in the area around the Koko Nor (Qinghai Hu; “Blue Lake”), he defeated the Tuyuhun people, who from time to time raided the border territories.
By the late 580s Wendi’s state was stable and secure enough for him to take the final step toward reunifying the whole country. In 587 he dethroned the emperor of the Hou (Later) Liang, the state that had ruled the middle Yangtze valley as a puppet of the Bei Zhou since 555. In 589 he overwhelmed the last southern dynasty, the Chen, which had put up only token resistance. Several rebellions against the Sui regime subsequently broke out in the south, but these were easily quelled. Wendi now ruled over a firmly reunited empire.