of the seventh century, a new political unit had formed in northern Tibet, the T’u-fan, who also seem to have had an upper class of Turks and Mongols and a Tibetan lower class.  Just as in the Han period, Chinese policy was bound to be directed to preventing a union between Turks and Tibetans.  This, together with commercial interests, seems to have been the political motive of the Chinese Turkestan policy under the T’ang.

3 Conquest of Turkestan and Korea.  Summit of power

The Turkestan wars began in 639 with an attack on the city-state of Kao-ch’ang (Khocho).  This state had been on more or less friendly terms with North China since the Toba period, and it had succeeded again and again in preserving a certain independence from the Turks.  Now, however, Kao-ch’ang had to submit to the western Turks, whose power was constantly increasing.  China made that submission a pretext for war.  By 640 the whole basin of Turkestan was brought under Chinese dominance.  The whole campaign was really directed against the western Turks, to whom Turkestan had become subject.  The western Turks had been crippled by two internal events, to the advantage of the Chinese:  there had been a tribal rising, and then came the rebellion and the rise of the Uighurs (640-650).  These events belong to Turkish history, and we shall confine ourselves here to their effects on Chinese history.  The Chinese were able to rely on the Uighurs; above all, they were furnished by the Toeloes Turks with a large army, with which they turned once more against Turkestan in 647-48, and now definitely established their rule there.

The active spirit at the beginning of the T’ang rule had not been the emperor but his son Li Shih-min, who was not, however, named as heir to the throne because he was not the eldest son.  The result of this was tension between Li Shih-min and his father and brothers, especially the heir to the throne.  When the brothers learned that Li Shih-min was claiming the succession, they conspired against him, and in 626, at the very moment when the western Turks had made a rapid incursion and were once more threatening the Chinese capital, there came an armed collision between the brothers, in which Li Shih-min was the victor.  The brothers and their families were exterminated, the father compelled to abdicate, and Li Shih-min became emperor, assuming the name T’ai Tsung (627-649).  His reign marked the zenith of the power of China and of the T’ang dynasty.  Their inner struggles and the Chinese penetration of Turkestan had weakened the position of the Turks; the reorganization of the administration and of the system of taxation, the improved transport resulting from the canals constructed under the Sui, and the useful results of the creation of great administrative areas under strong military control, had brought China inner stability and in consequence external power and prestige.  The reputation which she then obtained as the most powerful state of the Far East endured