During the 750s there was a steady reversal of Tang military fortunes. In the far west the overextended imperial armies had been defeated by the Arabs in 751 on the Talas River. In the southwest a campaign against the new state of Nanzhao had led to the almost total destruction of an army of 50,000 men. In the northeast the Chinese had lost their grip on the Manchuria-Korea border with the emergence of the new state of Parhae in place of Koguryŏ, and the Khitan and Xi peoples in Manchuria constantly caused border problems. The Tibetans in the northwest were kept in check only by an enormously expensive military presence. The principal military forces were designed essentially for frontier defense.
Thus, the end of Xuanzong’s reign was a time when the state was in a highly unstable condition. The central government was dangerously dependent on a small group of men operating outside the regular institutional framework, and an overwhelming preponderance of military power was in the hands of potentially rebellious commanders on the frontiers, against whom the emperor could put into the field only a token force of his own and the troops of those commanders who remained loyal.
Late Tang (755–907)
The rebellion of An Lushan in 755 marked the beginning of a new period. At first the rebellion had spectacular success. It swept through the northeastern province of Hebei, captured the eastern capital, Luoyang, early in 756, and took the main Tang capital, Chang’an, in July of the same year. The emperor fled to Sichuan, and on the road his consort Yang Guifei and other members of the Yang faction who had dominated his court were killed. Shortly afterward the heir apparent, who had retreated to Lingwu in the northwest, himself usurped the throne. The new emperor, Suzong (reigned 756–762), was faced with a desperately difficult military situation. The rebel armies controlled the capital and most of Hebei and Henan. In the last days of his reign, Xuanzong had divided the empire into five areas, each of which was to be the fief of one of the imperial princes. Prince Yong, who was given control of the southeast, was the only one to take up his command; during 757 he attempted to set himself up as the independent ruler of the crucially important economic heart of the empire in the Huai and Yangtze valleys but was murdered by one of his generals.
An Lushan himself was murdered by a subordinate early in 757, but the rebellion was continued, first by his son and then by one of his generals, Shi Siming, and his son Shi Chaoyi; it was not finally suppressed until 763. The rebellion had caused great destruction and hardship, particularly in Henan. The final victory was made possible partly by the employment of Uighur mercenaries, whose insatiable demands remained a drain on the treasury well into the 770s, partly by the failure of the rebel leadership after the death of the able Shi Siming, and partly by the policy of clemency adopted toward the rebels after the decisive campaign in Henan in 762. The need for a speedy settlement was made more urgent by the growing threat of the Tibetans in the northwest. The latter, allied with the Nanzhao kingdom in Yunnan, had exerted continual pressure on the western frontier and in 763 occupied the whole of present-day Gansu. Late in 763 they actually took and looted the capital. They continued to occupy the Chinese northwest until well into the 9th century. Their occupation of Gansu signaled the end of Chinese control of the region.
Provincial separatism
The post-rebellion settlement not only pardoned several of the most powerful rebel generals but also appointed them as imperial governors in command of the areas they had surrendered. Hebei was divided into four new provinces, each under surrendered rebels, while Shandong became the province of An Lushan’s former garrison army from Pinglu in Manchuria, which had held an ambivalent position during the fighting. The central government held little power within these provinces. The leadership was decided within each province, and the central government in its appointments merely approved faits accomplis. Succession to the leadership was frequently hereditary. For all practical purposes, the northeastern provinces remained semi-independent throughout the later part of the Tang era. They had been among the most populous and productive parts of the empire, and their semi-independence was not only a threat to the stability of the central government but also represented a huge loss of revenue and potential manpower.
Provincial separatism also became a problem elsewhere. With the general breakdown of the machinery of central administration after 756, many of the functions of government were delegated to local administrations. The whole empire was now divided into provinces (dao), which formed an upper tier of routine administration. Their governors had wide powers over subordinate prefectures and counties. The new provincial governments were of two main types.
In northern China (apart from the semiautonomous provinces of the northeast, which were a special category) most provincial governments were military, their institutions closely modeled on those set up on the northern frontier under Xuanzong. The military presence was strongest in the small frontier-garrison provinces that protected the capital, Chang’an, from the Tibetans in Gansu and in the belt of small, heavily garrisoned provinces in Henan that protected China—and the canal from the Huai and Yangtze valleys, on which the central government depended for its supplies—from the semiautonomous provinces. Military governments were also the rule in Sichuan, which continued to be menaced by the Tibetans and Nanzhao, and in the far south in Lingnan.
In central and southern China, however, the provincial government developed into a new organ of the civil bureaucracy. The civil governors of the southern provinces were regularly appointed from the bureaucracy, and it became customary to appoint to these posts high-ranking court officials who were temporarily out of favour.
All the new provinces had considerable latitude of action, particularly during the reigns of Suzong and Daizong, when central power was at a low ebb. There was a general decentralization of authority. The new provinces had considerable independence in the fields of finance, local government, law and order, and military matters.
Under Daizong (reigned 762–779) the court was dominated by the emperor’s favourite, Yuan Zai, and by the eunuchs who now began to play an increasing role in Tang politics. A succession of eunuch advisers not only rivaled in influence the chief ministers but even exerted influence over the military in the campaigns of the late 750s and early 760s. Under Daizong many of the regular offices of the administration remained unfilled, while the irregularities encouraged by Yuan Zai and his clique in the appointment of officials led to an increasing use of eunuchs in secretarial posts and to their increasing dominance over the emperor’s private treasury.
The central government did achieve some success in finance. The old fiscal system with its taxes and labour services had been completely disrupted by the breakdown of authority and by the vast movements of population. The revenues increasingly came to depend on additional taxes levied on cultivated land or on property, and the government attempted to raise more revenue from the urban population. But its survival depended on the revenues it drew from central China, the Huai valley, and the lower Yangtze. Those revenues were sent to the capital by means of a reconstructed and improved canal system maintained out of the new government monopoly on salt. By 780 the salt monopoly was producing a major part of the state’s central revenues, in addition to maintaining the transportation system. The salt and transportation administration was controlled by an independent commission centred in Yangzhou, near the mouth of the Yangtze, and this commission gradually took over the entire financial administration of southern and central China.