or Su Tsung died, in 762, Tengri, the khan of the Uighurs,
decided to make himself ruler over China. The events of the preceding
years had shown him that China alone was entirely defenceless. Part of
the court clique supported him, and only by the intervention of P'u-ku
Huai-en, who was related to Tengri by marriage, was his plan frustrated.
Naturally there were countless intrigues against P'u-ku Huai-en. He
entered into alliance with the Tibetan T'u-fan, and in this way the
union of Turks and Tibetans, always feared by the Chinese, had come into
existence. In 763 the Tibetans captured and burned down the western
capital, while P'u-ku Huai-en with the Uighurs advanced from the north.
Undoubtedly this campaign would have been successful, giving an entirely
different turn to China's destiny, if P'u-ku Huai-en had not died in 765
and the Chinese under Kuo Tzu-i had not succeeded in breaking up the
alliance. The Uighurs now came over into an alliance with the Chinese,
and the two allies fell upon the Tibetans and robbed them of their
booty. China was saved once more.

Friendship with the Uighurs had to be paid for this time even more
dearly. They crowded into the capital and compelled the Chinese to buy
horses, in payment for which they demanded enormous quantities of
silkstuffs. They behaved in the capital like lords, and expected to be
maintained at the expense of the government. The system of military
governors was adhered to in spite of the country's experience of them,
while the difficult situation throughout the empire, and especially
along the western and northern frontiers, facing the Tibetans and the
more and more powerful Kitan, made it necessary to keep considerable
numbers of soldiers permanently with the colours. This made the military
governors stronger and stronger; ultimately they no longer remitted any
taxes to the central government, but spent them mainly on their armies.
Thus from 750 onward the empire consisted of an impotent central
government and powerful military governors, who handed on their
positions to their sons as a further proof of their independence. When
in 781 the government proposed to interfere with the inheriting of the
posts, there was a great new rising, which in 783 again extended as far
as the capital; in 784 the T'ang government at last succeeded in
overcoming it. A compromise was arrived at between the government and
the governors, but it in no way improved the situation. Life became