At the beginning of Hsuean Tsung's reign the capital had been in the east at Loyang; then it was transferred once more to Ch'ang-an in the west due to pressure of the western gentry. The emperor soon came under the influence of the unscrupulous but capable and energetic Li Lin-fu, a distant relative of the ruler. Li was a virtual dictator at the court from 736 to 752, who had first advanced in power by helping the concubine Wu, a relative of the famous empress Wu, and by continually playing the eastern against the western gentry. After the death of the concubine Wu, he procured for the emperor a new concubine named Yang, of a western family. This woman, usually called "Concubine Yang" (Yang Kui-fei), became the heroine of countless stage-plays and stories and even films; all the misfortunes that marked the end of Hsuean Tsung's reign were attributed solely to her. This is incorrect, as she was but a link in the chain of influences that played upon the emperor. Naturally she found important official posts for her brothers and all her relatives; but more important than these was a military governor named An Lu-shan (703-757). His mother was a Turkish shamaness, his father, a foreigner probably of Sogdian origin. An Lu-shan succeeded in gaining favour with the Li clique, which hoped to make use of him for its own ends. Chinese sources describe him as a prodigy of evil, and it will be very difficult today to gain a true picture of his personality. In any case, he was certainly a very capable officer. His rise started from a victory over the Kitan in 744. He spent some time establishing relations with the court and then went back to resume operations against the Kitan. He made so much of the Kitan peril that he was permitted a larger army than usual, and he had command of 150,000 troops in the neighbourhood of Peking. Meanwhile Li Lin-fu died. He had sponsored An as a counterbalance against the western gentry. When now, within the clique of Li Lin-fu, the Yang family tried to seize power, they turned against An Lu-shan. But he marched against the capital, Ch'ang-an, with 200,000 men; on his way he conquered Loyang and made himself emperor (756: Yen dynasty). T'ang troops were sent against him under the leadership of the Chinese Kuo Tzu-i, a Kitan commander, and a Turk, Ko-shu Han.

The first two generals had considerable success, but Ko-shu Han, whose task was to prevent access to the western capital, was quickly defeated and taken prisoner. The emperor fled betimes, and An Lu-shan captured Ch'ang-an. The emperor now abdicated; his son, emperor Su Tsung (756-762), also fled, though not with him into Szechwan, but into north-western Shensi. There he defended himself against An Lu-shan and his capable general Shih Ssu-ming (himself a Turk), and sought aid in Central Asia. A small Arab troop came from the caliph Abu-Jafar, and also small bands from Turkestan; of more importance was the arrival of Uighur cavalry in substantial strength. At the end of 757 there was a great battle in the neighbourhood of the capital, in which An Lu-shan was defeated by the Uighurs; shortly afterwards he was murdered by one of his eunuchs. His followers fled; Loyang was captured and looted by the Uighurs. The victors further received in payment from the T'ang government 10,000 rolls of silk with a promise of 20,000 rolls a year; the Uighur khan was given a daughter of the emperor as his wife. An Lu-shan's general, the Turk Shih Ssu-ming, entered into An Lu-shan's heritage, and dominated so large a part of eastern China that the Chinese once more made use of the Uighurs to bring him down. The commanders in the fighting against Shih Ssu-ming this time were once more Kuo Tzu-i and the Kitan general, together with P'u-ku Huai-en, a member of a Toeloes family that had long been living in China. At first Shih Ssu-ming was victorious, and he won back Loyang, but then he was murdered by his own son, and only by taking advantage of the disturbances that now arose were the government troops able to quell the dangerous rising.

In all this, two things seem interesting and important. To begin with, An Lu-shan had been a military governor. His rising showed that while this new office, with its great command of power, was of value in attacking external enemies, it became dangerous, especially if the central power was weak, the moment there were no external enemies of any importance. An Lu-shan's rising was the first of many similar ones in the later T'ang period. The gentry of eastern China had shown themselves entirely ready to support An Lu-shan against the government, because they had hoped to gain advantage as in the past from a realm with its centre once more in the east. In the second place, the important part played by aliens in events within China calls for notice: not only were the rebels An Lu-shan and Shih Ssu-ming non-Chinese, but so also were most of the generals opposed to them. But they regarded themselves as Chinese, not as members of another national group. The Turkish Uighurs brought in to help against them were fighting actually against Turks, though they regarded those Turks as Chinese. We must not bring to the circumstances of those times the present-day notions with regard to national feeling.