The emperor Hsüan-tsung, longest-reigning of all the T'ang monarchs, was an immensely capable ruler, who restored his dynasty to a new peak of power after decades of usurpation, weakened authority and corruption. To the Chinese living through the troubled and disturbed decades which followed his abdication, his reign represented a golden age of departed glories, an era of good government, peace and prosperity, equally successful at home and abroad. Yet his reign ended in tragedy, and in disasters largely resulting from his own actions and policies which almost destroyed the dynasty. To the historians who wrote the record of his reign in the late 750s he was a tragic hero, whose reign had begun in splendour, but who had later been led astray by ambition and hubris into overstraining his empire's administration and resources, and who then completed its ruin by withdrawal from active participation in its government.

All were agreed, however, that he was a ruler out of the ordinary, who left his indelible print upon the history of his times. He was, moreover, a man of many parts, a skilled musician, a poet, a good calligrapher, patron of many artists and writers. He was also deeply versed in Taoist philosophy, of which he became a major patron, and – in spite of his early measures against the Buddhist establishment – later became deeply involved in Esoteric Buddhism. As a person he seems to have enjoyed deep friendship with his brothers and family members, and even the formal records of his reign portray a man of great personal warmth, close attachment to his advisers, directness and passion.

This volume is the first of two devoted to the Sui and T'ang dynasties (581–907). It is designed to provide the reader with a narrative account of this complex period, during which China underwent far-reaching changes in political institutions, in her relations with the neighbouring countries, in social organization, in the economy and in every sphere of intellectual, religious and artistic life. The broader issues in institutions, social and economic change and in intellectual developments are dealt with in detail in Volume 4 which also contains a bibliography for both volumes.

A glance at this bibliography will show that a wealth of modern scholarship has been devoted to the T'ang. Chinese scholars have been attracted to the period as one of the high points of Chinese political power and influence, and as one of extraordinary achievements in every field of culture and the arts. Japanese scholars have been drawn to the Sui and T'ang not simply because of the intrinsic interest of the period, but also because it was during these dynasties that Japan was most deeply influenced by Chinese institutions. Consequently Japanese scholars have had a deep and instinctive understanding of Sui and T'ang China which provided so much of the fabric of their own state structure, laws and institutions, art, literature and even of their written language. Western scholars too have long been fascinated by the period – the first full scale political history of the T'ang in a European language was completed by Father Antoine Gaubil SJ in 1753 – and in recent decades have begun to make their own distinctive contribution to the understanding of T'ang China.

The future T'ai-tsung, Li Shih-min, the second son of Kao-tsu, was born in the year 600 in Wu-kung county in modern Shensi. His mother was a member of an extremely powerful clan, the Tou. Her elder sister was the consort of Yang Kuang, the future Sui emperor Yang-ti. Their clan, which like the Sui and T'ang imperial houses was of partially alien origin (their original surname was Ho-tou-ling), continued to be very influential throughout the early T'ang, producing two empresses, six consorts of royal princes, eight husbands of royal princesses, and a great number of officials of the highest ranks. T'ai-tsung's mother had been brought up at the court of her uncle, the emperor Wu-ti of the Northern Chou (whose younger sister was her mother), where Li Yüan is said to have won her hand in an archery contest. She died in 614.

During his childhood Li Shih-min was, of course, simply a son of a nobleman, and thus would not have received any special preparation as a potential ruler. He certainly received the upper-class Confucian education typical of the time: later, as emperor he proved to be well versed in classical and historical learning and was a calligrapher of note. The Li clan, bearer of a strong northern tradition, was naturally Buddhist, and several of Kao-tsu's sons bore Buddhist childhood names. But, as with most noblemen of mixed Chinese and Turkish blood, the emphasis of T'ai-tsung's early education was upon the martial arts – particularly archery and horsemanship.

In 617 Li Yüan (566–635), the Duke of T'ang and one of the most powerful Sui generals, joined the scores of rebels who had arisen in the waning years of the Sui dynasty. His armies marched on the Sui capital, overwhelmed its defences, and took the city. There, six months later, he founded a new dynasty which was to endure for almost three centuries, and would rank alongside the Han as one of China's two golden ages of empire. As Li Yüan went on to impose firm central authority throughout the country, he was fortunate in being the heir to the great achievements of the Sui, who, barely three decades before, had brought centuries of disunion to an end. The institutions of his new dynasty were established on the solid foundations left by his predecessors.

Like the majority of rebel leaders throughout Chinese history who succeeded in founding dynasties of their own, Li Yüan was not a commoner but a nobleman of distinguished lineage. His ancestry can be traced with certainty as far as his grandfather, Li Hu, one of the ‘Eight Pillars of State’ (Pa Kuo-chu), the chief commanders associated with Yü-wen T'ai in the foundation of the Northern Chou state in the 550s. At that time the Li clan was centred on Wu-ch'uan chen, a garrison established by the Toba state of Northern Wei inside the Great Wall near modern Tat'ung, which was also the home of Yü-wen T'ai.

The powerful decentralized provincial order which emerged in China after the middle of the eighth century was a direct result of the An Lu-shan rebellion of 755–63. After the founding itself, the rebellion is without doubt the most significant event in the history of the dynasty. It transformed a centralized, rich, stable and far-flung empire into a struggling, insecure and divided one. It has long been treated by historians as a turning-point in T'ang history; in recent decades it has even been treated as a major turning point in Chinese history as a whole. Yet, there is a striking disparity between the event and its consequences. Although such a major internal upheaval was bound to have grave and far-reaching effects, could what was essentially a military event have brought about the profound changes which differentiate the second half of the dynasty from the first so completely?

In reality, the changed situation of China after An Lu-shan's rising resulted not merely from the rebellion alone, but had its roots in developments long under way. As preceding chapters in this volume have shown, T'ang political institutions had undergone significant modifications since the beginning of the dynasty. These changes already anticipated the emergence of forms of government quite different in character from those of early T'ang. But it is imperative to distinguish these long-term changes from the specific origins of the rebellion itself. There was nothing inevitable about this event, even though when it came, it caused a tremendous disruption and acted as a powerful catalyst.