e-hun, and then himself
attacked the latter, so destroying their power. The T'u-yue-hun were a
people living in the extreme north of Tibet, under a ruling class
apparently of Hsien-pi origin; the people were largely Tibetan. The
purpose of the conquest of the T'u-yue-hun was to safeguard access to
Central Asia. An effective Turkestan policy was, however, impossible so
long as the Turks were still a formidable power. Accordingly, the
intrigues that aimed at keeping the two sections of Turks apart were
continued. In 615 came a decisive counter-attack from the Turks. Their
khan, Shih-pi, made a surprise assault on the emperor himself, with all
his following, in the Ordos region, and succeeded in surrounding them.
They were in just the same desperate situation as when, eight centuries
earlier, the Chinese emperor had been beleaguered by Mao Tun. But the
Chinese again saved themselves by a trick. The young Chinese commander,
Li Shih-min, succeeded in giving the Turks the impression that large
reinforcements were on the way; a Chinese princess who was with the
Turks spread the rumour that the Turks were to be attacked by another
tribe--and Shih-pi raised the siege, although the Chinese had been
entirely defeated.

In the Sui period the Chinese were faced with a further problem. Korea
or, rather, the most important of the three states in Korea, had
generally been on friendly terms with the southern state during the
period of China's division, and for this reason had been more or less
protected from its North Chinese neighbours. After the unification of
China, Korea had reason for seeking an alliance with the Turks, in order
to secure a new counterweight against China.

A Turco-Korean alliance would have meant for China a sort of
encirclement that might have grave consequences. The alliance might be
extended to Japan, who had certain interests in Korea. Accordingly the
Chinese determined to attack Korea, though at the same time negotiations
were set on foot. The fighting, which lasted throughout the Sui period,
involved technical difficulties, as it called for combined land and sea
attacks; in general it brought little success.

3 _Reasons for collapse_

The continual warfare entailed great expense, and so did the intrigues,
because they depended for their success on bribery. Still more expensive
were the great canal works. In addition to this, the emperor Yang Ti,
unlike his father, was very extravagant. He built enormous