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. [Illustration: Map 5: The T'ang realm (_about A.D. 750_)] 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 and had been able to obtain anything they wanted from him, now began to desert him and set up pretenders. From 615 onward, after the defeat at the hands of the Turks, risings broke out everywhere. The emperor had to establish his government in the south, where he felt safer. There, however, in 618, he was assassinated by conspirators led by Toba of the Yü-wen family. Everywhere now independent governments sprang up, and for five years China was split up into countless petty states. (B) The T'ang dynasty (A.D. 618-906) 1 _Reforms and decentralization_