The reign of Taizong (626–649), known traditionally as the “era of good government of Zhenguan,” was not notable for innovations in administration. Generally, his policies developed and refined those of his father’s reign. The distinctive element was the atmosphere of his administration and the close personal interplay between the sovereign and his unusually able team of Confucian advisers. It approached the Confucian ideal of a strong, able, energetic, yet fundamentally moral king seeking and accepting the advice of wise and capable ministers, advice that was basically ethical rather than technical. Some important changes in political organization were begun during his reign and were continued throughout the 7th century. The court remained almost exclusively the domain of men of aristocratic birth. But Taizong attempted to balance the regional groups among the aristocracy so as to prevent any single region from becoming dominant. They comprised the Guanlong group from the northwest, the Daibei group from Shanxi, the Shandong group from Hebei, and the southern group from the Yangtze valley. The most powerful Hebei clans were excluded from high office, but Taizong employed members of each of the other groups and of the lesser northeastern aristocracy in high administrative offices as well as in his consultative group of scholars.

A second change was the use of the examination system on a large scale. The Sui examinations had already been reestablished under Gaozu, who had also revived the Sui system of high-level schools at the capital. Under Taizong the schools were further expanded and new ones established. Measures were taken to standardize their curriculum, notably completing an official orthodox edition of the Classics with a standard commentary in 638. The schools at the capital were mostly restricted to the sons of the nobility and of high-ranking officials. Other examination candidates, however, came from the local schools. The examinations were in principle open to all, but they provided relatively few new entrants to the bureaucracy. Most officials still entered service by other means—hereditary privilege as sons of officials of the upper ranks or promotion from the clerical service or the guards. The examinations demanded a high level of education in the traditional curriculum and were largely used as an alternative method of entry by younger sons of the aristocracy and by members of lesser families with a scholar-official background. Moreover, personal recommendation, lobbying examiners, and often a personal interview by the emperor played a large part. Even in late Tang times, not more than 10 percent of officials were recruited by the examinations. The main effect of the examination system in Tang times was to bring into being a highly educated court elite within the bureaucracy, to give members of locally prominent clans access to the upper levels of the bureaucracy, and in the long term to break the monopoly of political power held by the upper aristocracy. Employing persons dependent for their position on the emperor and the dynasty, rather than on birth and social standing, made it possible for the Tang emperors to establish their own power and independence.

In the early years there was a great debate as to whether the Tang ought to reintroduce the feudal system used under the Zhou and the Han, by which authority was delegated to members of the imperial clan and powerful officials and generals who were enfeoffed with hereditary territorial jurisdictions. Taizong eventually settled on a centralized form of government through prefectures and counties staffed by members of a unified bureaucracy. The Tang retained a nobility, but its “fiefs of maintenance” were merely lands whose revenues were earmarked for its use and gave it no territorial authority.

Taizong continued his father’s economic policies, and government remained comparatively simple and cheap. He attempted to cut down the bureaucratic establishment at the capital and drastically reduced the number of local government divisions. The country was divided into 10 provinces, which were not permanent administrative units but “circuits” for occasional regional inspections of the local administrations; these tours were carried out by special commissioners, often members of the censorate, sent out from the capital. This gave the central government an additional means of maintaining standardized and efficient local administration. Measures to ensure tax relief for areas stricken by natural disasters, and the establishment of relief granaries to provide adequate reserves against famine, helped to ensure the prosperity of the countryside. Taizong’s reign was a period of low prices and general prosperity.

Taizong was also successful in his foreign policy. In 630 the eastern Turks were split by dissension among their leadership and by the rebellion of their subject peoples. Chinese forces invaded their territories, totally defeated them, and captured their khan, and Taizong was recognized as their supreme sovereign, the “heavenly khan.” A large number of the surrendered Turks were settled on the Chinese frontier, and many served in the Tang armies. A similar policy of encouraging internal dissension was later practiced against the western Turks, who split into two separate khanates for a while. In 642–643 a new khan reestablished a degree of unified control with Chinese support and agreed to become a tributary of the Chinese. To seal the alliance, Taizong married him to a Chinese princess.

The eclipse of Turkish power enabled Taizong to extend his power over the various small states of the Tarim Basin. By the late 640s a Chinese military administration had extended westward even beyond the limits of present-day Xinjiang. To the north, in the region of the Orhon River and to the north of the Ordos (Mu Us) Desert, the Tang armies defeated the Xueyantou (Syr Tardush), former vassals of the eastern Turks, who became Tang vassals in 646. The Tuyuhun in the region around Koko Nor caused considerable trouble in the early 630s. Taizong invaded their territory in 634 and defeated them, but they remained unsubdued and invaded Chinese territory several times.

The Chinese western dominions now extended farther than in the great days of the Han. Trade developed with the West, with Central Asia, and with India. The Chinese court received embassies from Sasanian Persia and from the Byzantine Empire. The capital was thronged with foreign merchants and foreign monks and contained a variety of non-Chinese communities. The great cities had Zoroastrian, Manichaean, and Nestorian temples, along with the Buddhist monasteries that had been a part of the Chinese scene for centuries.

Taizong’s only failure in foreign policy was in Korea. The northern state of Koguryŏ had sent tribute regularly, but in 642 there was an internal coup; the new ruler attacked Silla, another Tang vassal state in southern Korea. Taizong decided to invade Koguryŏ, against the advice of most of his ministers. The Tang armies, in alliance with the Khitan in Manchuria and the two southern Korean states Paekche and Silla, invaded Koguryŏ in 645 but were forced to withdraw with heavy losses. Another inconclusive campaign was waged in 647, and the end of Taizong’s reign was spent in building a vast fleet and making costly preparations for a final expedition.

Taizong’s last years were also marked by a decline in the firm grasp of the emperor over politics at his court. In the 640s a bitter struggle for the succession developed when the designated heir was passed over and eventually banished for behavior that Taizong deemed unacceptable. The court split into factions supporting various candidates. The final choice, Li Zhi, prince of Jin (reigned 649–683; temple name Gaozong) was a weak character, but he had the support of the most powerful figures at court.