North and south China were politically reunited in 589 when the Sui Dynasty (581-618 AD) defeated the last of the Southern Dynasties. After only two generations, the Sui was itself replaced by the Tang Dynasty (618-907AD), but progress toward cultural, economic and political reunification continued, especially under three forceful rulers: Taizong, Empress Wu and Xuanzong. The capital cities of Chang'an and Luoyang attracted people not only from all parts of China but also from all parts of Asia. The arts, and above all poetry, thrived in this environment. After the massive rebellion of the general An Lushan wracked China in the mid-eighth century, many of the centralizing features of the government were abandoned, and power fell more and more to regional military governors. Yet late Tang should not be viewed simply in terms of dynastic decline, as art and culture continued to flourish.

That reunification came about from the north is not surprising, since by the fifth century the south had largely abandoned hope of reconquering the north. Reunification was delayed, however, by the civil war in the north after 523 . This changed in 577 when the Northern Zhou Dynasty defeated the Northern Qi, which freed up its armies to take on the south. The rulers of Northern Zhou were not Chinese, though in this period ethnicity was fluid and intermarriage among ethnic groups was common. Generally ethnicity was considered to be passed down with family names on the father's side, but family names could be changed. Yang Jian, the founder of the Sui Dynasty, claimed descent from Han Chinese, but Yang was one of the names given to Xianbei settlers in the fifth century, so his ancestors might well have been Xianbei. Yang Jian's daughter married into the non-Chinese Yuwen family, the Northern Zhou royal house, after which Yang Jian usurped the throne from his daughter's young son and proclaimed himself emperor of the new Sui dynasty. He was known as Wendi, the "cultured emperor" (r. 581-604). Wendi presided over the reunification of China, building thousands of boats to compete for control of the Yangzi River. Some of those ships were manned by aborigines from southeastern Sichuan, recently conquered by the Sui. By late 588 , Sui had over half a million troops deployed along the north bank of the Yangzi, from Sichuan to the Pacific Ocean. Within three months, Sui had captured Nanjing, and the rest of the south soon submitted. After capturing Nanjing, the Sui commanders forced the nobles and officials resident there to move to the new Sui capital at Chang'an.

Both Wendi and his empress were pious Buddhists and drew on Buddhism to legitimise the Sui Dynasty. Wendi portrayed himself as a Cakravartin king, a Buddhist monarch who used military force to defend the Buddhist faith. In 601 , in imitation of the Buddhist Indian king Ashoka the Great, he had relics of the Buddha distributed to temples throughout the country. Both Wendi and his successor, Yangi (r. 604-617 ), had grand ambitions to rebuild an empire comparable to the Han. The Sui helped tie north and south China together by a major feat of construction: the Grand Canal. Built by conscripted laborers, the canal linked the Yellow and Yangzi rivers. In later dynasties, this canal would be extended northeast as far as Beijing and to the south as far as Hangzhou. The Suicanal was 130 feet wide and ran parallel to an imperial road with relay posts and supply granaries. Easy water transport made it much easier to ship tax grain from the south to the centers of political and military power in north China. However, both Sui emperors viewed their empire as incomplete because they had not recovered the parts of modern Korea and Vietnam that the Han Dynasty had held. The Hanoi area was easily recovered in 602 , and the few years later the Sui army pushed farther south. Although the Sui troops were victorious in the Champa region of southern Vietnam, many succumbed to disease, as northern soldiers did not have immunity to tropical diseases such as malaria.

Recovering northern Korea proved an elusive goal. The Korean state of Koguryo had its capital near modern Pyongyang and also held southern Manchuria was far as the Liao River. When in 598 AD, Koguryo troops joined a raid into Sui territory, Wendi ordered three hundred thousand troops to retaliate. However, the Sui army had to turn back when food supplies ran short. A supply fleet sent from Shandong lost many of its vessels in storms and accomplished nothing. Another attempt was made in 611 . Three hundred ships were built in Shandong and Yangdi himself traveled to the region of modern Beijing to oversee preparations. Reportedly, six hundred thousand men were conscripted and sent overland for the invasion. Again, however, supplies sent by ship failed to resupply them, and the vast majority of the soldiers sent across the Yalu River did not make it back to China. The cost to the Sui Dynasty of this military debacle was enormous. When floods, droughts and epidemics reached areas that had been hard pressed by conscription, army deserters turned into bandits. Nevertheless, Yangdi was determined to try a third time to take Korea. The 613 expedition crossed the Liao River and set siege to Koguryo strongholds, but the campaign was cut short when word reached the emperor of a major rebellion in central China. Still, in 614 Yangdi ordered the Korea campaign continued. This time the naval force made enough progress that the Koguryo king sought for peace and Yangdi could claim victory. When the Korean king failed to appear at the Sui court as he had been commanded, Yangdi began mobilizing for a fourth campaign in 615. Unrest was growing so serious, however, that nothing came of it. Yangdi, by leading the Korean campaign himself, was personally humiliated by their failures. The imperial dreams of the Sui emperors had resulted in exhaustion and unrest among the Chinese people.

With the Sui government unraveling, power was seized at the local level by several kinds of actors: bandit leaders and local elites trying to organize defense of their own. The contender who eventually founded the Tang Dynasty was Li Yuan, the Sui governor of Taiyuan, and his general son, Li Shimin, known respectively by the imperial names Gaozu (r. 618-626) and Taizong (r. 626-649). The Sui emperor Yangdi and Taizong were in fact first cousins. Though probably of non-Chinese ethnicity, the Tang imperial family presented themselves as Chinese by descent, much as the Sui imperial family had. Taizong, was not Gaozu's original heir, but in 626 he ambushed and killed his two brothers, one of whom was the heir apparent. Despite these violent beginnings, Taizong proved a capable monarch, who issued a new legal code which would have great influence on the legal systems of China, Vietnam, Korea and Japan for many years to come. The Tang turned away from the military culture of the Northern Dynasties and sought officials steeped in Confucian learning. Government schools were founded to prepare young men for service in the government and recruitment through the examination system grew in importance. In the Tang system, there were two principal examinations. One, known as the mingjing, tested knowledge of the Confucian classics, while the other tested not memorization but literary skill. It tested the ability to compose formal styles of poetry as well as essays on political questions. This examination, known as the jinshi, was more demanding, but brought more prestige.

During the sixth century, a new ethnic group emerged as the dominant group on the Inner Asian frontier: the Turks. To keep them in check, the Tang government used all the old diplomatic and military strategies. They repaired fortifications, received trade and tribute missions, sent princesses as brides, and instigated conflict between different tribes. Eventually, many ethnic Turks were recruited into the Tang armies. In 630, the Tang wrested control of Shaanxi and southern Mongolia from the Turks, and Taizong himself was crowned Great Khan of the Turks. For the next half century, Tang China dominated the steppe. Turks were settled in the Ordos region, as the Xiongnu had been in Han times, and several thousands of Turkist families came to live in Chang'an. Joint Chinese-Turkish campaigns into Central Asia in the 640s and 650s resulted in China regaining overlordship of the region much as it had during the Han Dynasty.

The Tang retained the city of Chang'an, which the Sui had built, as its capital and made Luoyang its secondary capital. Both cities became great metropolises, with Chang'an and its suburbs growing to more than 2 million inhabitants. At these cosmopolitan cities, knowledge of the outside world was stimulated by the presence of envoys, merchants and pilgrims from Central Asia, Japan, Korea, Vietnam, and Tibet, among other places. Many religions were practiced, including Christianity, Manichaeism, Zoroastrianism, Judaism and Islam, although none of them influencea the Chinese population the way Buddhism had a few centuries earlier. In both the sacred and secular spheres, the introduction of new instruments and tunes from India, Iran and Central Asia brought about a major transformation in Chinese music. In Tang times, Buddhism fully penetrated Chinese daily life. Buddhist monasteries ran schools for children, provided lodging for travelers and offered scholars and officials a place to gather for social occasions. Merchants entrusted their money and wares to monasteries for safekeeping, in effect transforming the monasteries into banks and warehouses. The wealthy often donated money or land to monasteries, making them large landlords. In the Tang period, stories of Buddhist origin were spread by monks, who told stories to a mostly illiterate audience. One of the best known of these stories concered a man named Mulian who journeyed to the underworld to save his mother from her suffering there. The popularity of this story gave rise to the Chinese ghost festival on the fifteenth day of the seventh month. On that day, Buddhists and non-Buddhists alike would put out food to feed hungry ghosts suffering in the afterlife. At the intellectual level, Buddhism was developing in distinctly Chinese directions. Among the educated elite, the Chan school (known as Zen in Japan) gained popularity, especially in the north. The "northern" tradition of Chan emphasized meditation and monastic discipline. The "southern" tradition was even more iconoclastic, holding that enlightenment could be achieved suddenly through a flash of insight, even without prolonged meditation. In the late Tang period, opposition to Buddhism arose because its tax-exempt status aggravated the state's financial problems. In 845, more than 4,600 monasteries and 40,000 temples were closed down. The monastic tradition never fully recovered. Buddhism retained a strong hold among laypeople, and basic Buddhist ideas like karma and reincarnation became ingrained, but Buddhism was never again as central to Chinese life as it was in Tang times.

EMPRESS WU

The mid-Tang Dynasty saw several women rise to positions of great political power. Empress Wu (ca. 625-705) went so far as to take the throne herself. Although Wu entered Emperor Gaozong's palace in 651 as a lesser consort, within a few years she convinced him to demote his empress and promote herself in her place. Four years later Gaozong suffered a stroke, and Empress Wu began to make decisions in his place. By the AD670s, Empress Wu's oldest son, the heir apparent, was beginning to take stands on issues, even sometimes opposing his mother's ideas. When he died in 675, many suspected that she had poisoned him. After more than twenty years as a puppet ruler, Emperor Gaozong finally died in 683. The seventeen year old heir apparent, posthumously known as Zhongzong, took the throne. After six weeks, Empress Wu had him deposed because he tried to appoint his wife's father as chancellor. Another one of her sons, known as Ruizong, was then placed on the throne, but he was kept in a separate palace and rarely consulted. Now nearly sixty years old, Empress Wu began to use the Chinese term for the royal 'we'. Until 690 Empress Wu had been content to be the power behind the throne. That year, however, when she was about sixty-five years old, she brought about her son's abdication and declared herself empress of a new Zhou Dynasty. She became China's first and only female empress. She did not designate an heir, apparently unsure whether she should let one of her own sons succeed her or have succession go to a member of her natal Wu family. In 697, when she was over seventy, she had her eldest surviving son, Zhongzong, brought back from exile and made heir apparent. Still, all through her seventies she retained power. It was not until 705 when she was about eighty and too ill to get out of bed, that the high officials successfully pressured her to abdicate.

AN LUSHAN REBELLION AND ITS AFTERMATH

An Lushan was a half Sogdian, half Turk commander of the frontier army in Northern Hubei. He was a professional soldier from a family of soldiers, with experience fighting the Manchurian Khitans. When An Lushan rebelled in 755AD, he had an army of more than one hundred thousand veteran troops. They struck southward, headed towards Luoyang. The court, on getting news of the advance, began to raise an army, but the new recruits were no match for the veterans. With the fall of the capital imminent, the heir apparent left to raise troops in western Shaanxi and Emperor Xuanzong fled west towards Sichuan. The troops accompanying Xuanzong mutinied, and the heir apparent, in the meantime, was convinced by his followers to enthrone himself, which Xuanzong did not contest. How did the Tang Dynasty manage to recover from this disaster? They had to make many compromises. To recover the capital, the Tang called on the Uighurs, a Turkish people allied with the Tang. After the Uighurs took Chang'an from the rebels, they looted it and would not leave until they were paid off with huge quantities of silk. Thereafter, to keep the Uighurs from raiding, the Tang had to trade silk for horses at extortionate rates. Yet the Uighurs were only one of China's troublesome neighbors in this period. Antagonistic states were consolidating themselves all along Tang's borders, from Parhae on the northeast, to Tibet in the west, and Nanzhao on the southwestern Yunnan area. When Tang had to withdraw troops from the western frontier to fight An Lushan's forces, the Tibetans took advantage of the opportunity to claim overlordship of the Silk Road cities themselves. Although the Tibetan empire collapsed in 842 and the Uighur confederation broke up soon after that, the Tang court no longer had the ambition to dominate Central Asia. Tang did not respond when Nanzhao attacked the Tang prefectures in northern Vietnam, and though Tang sent an army to reassert control, the Vietnamese declared their independence in the tenth century.

After the rebellion of An Lushan, the Tang central government shared political and military power with the military governors. After 860, this system no longer worked to maintain order. Bandit gangs, some as large as small armies, roamed the countryside and set siege to walled cities. Such gangs smuggled illicit salt, ambushed merchants and tax convoys, and went on wild rampages throughout the countryside. During the century from 860 to 960, political and military power devolved to the local level. Any local strongman able to organize defense against rebels and bandits could declare himself king or even emperor. Many of these local rulers rose from very humble origins; one had started out as a mere merchant's slave. In the south, no self-proclaimed king ever consolidated more than the equivalent of one or two modern provinces. Thus, the situation known as the 'Ten Kingdoms' arose in south China. However, political fragmentation did not impair the economy of the south. In fact, in their eagerness to expand their tax bases, rulers of the southern kingdoms did their best to promote trade and tax it. In the north, many of the regional warlords were not Chinese, but Turks. Both Chang'an and Luoyang had been devastated by the fighting of the late Tang period, and Kaifeng, located at the mouth of the Grand Canal, became the leading city in north China. Yet none of the Five Dynasties that in succession held Kaifeng was able to build a stable government before being ousted by rivals. After a hundred years of political chaos, Emperor Taizu of the new Song Dynasty (r. 960-979 AD) ended the upheaval of the Ten Kingdoms and Five Dynasties period.