protectorate of two governors-general. Their leaders were admitted into
the Chinese army, and the sons of their nobles lived at the imperial
court. No doubt it was hoped in this way to turn the Turks into Chinese,
as had been done with the Toba, though for entirely different reasons.
More than a million Turks were settled in this way, and some of them
actually became Chinese later and gained important posts.

In general, however, this in no way broke the power of the Turks. The
great Turkish empire, which extended as far as Byzantium, continued to
exist. The Chinese success had done no more than safeguard the frontier
from a direct menace and frustrate the efforts of the supporters of the
Sui dynasty and the Toba dynasty, who had been living among the eastern
Turks and had built on them. The power of the western Turks remained a
lasting menace to China, especially if they should succeed in
co-operating with the Tibetans. After the annihilation of the T'u-yü-hun
by the Sui at the very beginning 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,