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 palaces and undertook long journeys throughout the empire with an immense following.  All this wrecked the prosperity which his father had built up and had tried to safeguard.  The only productive expenditure was that on the canals, and they could not begin to pay in so short a period.  The emperor’s continual journeys were due, no doubt, in part simply to the pursuit of pleasure, though they were probably intended at the same time to hinder risings and to give the emperor direct control over every part of the country.  But the empire was too large and too complex for its administration to be possible in the midst of journeying.  The whole of the chancellery had to accompany the emperor, and all the transport necessary for the feeding of the emperor and his government had continually to be diverted to wherever he happened to be staying.  All this produced disorder and unrest.  The gentry, who at first had so strongly supported the emperor