Economic Growth
The growth of religion during the Medieval Era allowed states to consolidate their power and grow stronger. While this was not appreciated by a people mourning the greatness of their past, this period of Chinese history was a critical formative period for important cultural and religious institutions. When China was reunified under the Sui Dynasty in 589 AD, this was the foundation upon which China was able to build the world's most advanced civilization. The Sui emperors (both of them) launched many national infrastructure projects which helped to realize Chinese reunification and grow the long-term economy. The most important of these projects was the Grand Canal which for the first time physically linked North and South China. These projects were deeply unpopular at the time due to the intense labor conscription, high death rate among workers, and high taxes they involved. This led to the downfall of the Sui Dynasty in 618 AD, but just a few years later in 624 AD, China was reunified by Li Yuan, Duke of Tang. The Tang Dynasty would be the second great dynasty to rule China and pushed her borders into the Middle East.
The Grand Canal, despite its divisive beginnings, would serve as an impressive statement of Chinese power for centuries, even to the present day. Its beauty was legendary, and its economic and political importance impossible to overstate to the nation. It physically unified China, and became the vital highway pouring trade and tourism between north and south. While the Great Wall has become an exotic symbol that Chinese and foreigners admire as a wonder of the world, the Grand Canal was the wonder of the world that ran through their own backyards nearly 500 years earlier.
The Tang emperors encouraged trade and built their capital Xian, into the most magnificent city in the world by nurturing the most cosmopolitan culture and the most vibrant monetary economy of the Medieval Era. An economy so successful, that when its political power faltered, it fell prey to its own wealthy aristocrats. But in terms of social development, China's economic sophistication explains why unique among the civilizations of the world, China emerged into the Renaissance before 1000 AD. The survival of South China during the Age of Division gave Chinese civilization a base from which to survive, incubate, and then expand under the Tang Dynasty as far as the Middle East. Where Arabs and Germans had to raise empires on lessons learned from the great Ancient Era powers, Chinese civilization Was one of the great Ancient Era powers. This head start and sophistication clearly showed.
Perhaps of equal importance, Chinese success was deeply rooted in Buddhism; few religions coexisted as neatly with learning and education. Like Muhammad's invocation to explore knowledge, Kung Fu Tzu prized intelligence and education. These principles would be absorbed into Chinese religion to the extent that China instituted the first national examination system in world history, scores were used to determine entrance to the university system and for government jobs as well. Education consisted of studying the Chinese classics of literature, wisdom, and moral conduct. The examination system was not a panacea, though popular literature of "noble peasants" scoring high government posts by virtue and good test scores was a popular theme. However, those with wealth could afford to hire teachers and tutors for their sons while the very poor could not even grant their boys much time to study; they were needed to help with farm labor. Nevertheless, the examination system was used to build a government meritocracy in which performance and excellence counted for more than any of the factors used by other civilizations (birth, family connections, race, religion, etc.) It was the most sophisticated and advanced government of Medieval Era and is one of the most important reasons directly responsible for the success of the Tang Emperors.
Tang armies also expanded China's borders throughout the North and South and then broke out along the Silk Road. Chinese armies would march across the Middle East until 751 AD when their furthest penetration yet encountered an army of the Abbasid Caliphate. The Battle of the Talas River is thus one of the most defining battles of the Medieval Era; Arab victory ensured their dominance throughout the Middle East and marked the peak of Tang Chinese expansion.
However, this is not the reason that the Tang Dynasty is still cherished by modern Chinese. In England and the United States today, school children study Shakespeare whose writings 500 years earlier are still considered mandatory reading for a complete education. Chinese children also read the literature of their ancestors; it's just a little older. 1300 years ago, Du Fu (712 - 770 AD) became almost instantly the most important poet in Chinese history, closely followed by Li Bai (701 - 762 AD) and Wang Wei (701 - 761 AD). Equivalent to the explosion of poets in Elizabethan London (or Augustan Rome which produced Vergil, Horace, Catullus, and a legion of other Roman poets), Xian during the Tang Dynasty hosted the greatest poets in Chinese history, poetic verses that are still on the lips of China's school children today.
All good things come to an end however. In 755 AD, the An Lushan rebellion, toppled the Tang Dynasty which fled south. Although the Tang emperors would eventually return, this storied flight colored perceptions of the Tang Dynasty ever after. Like the Emperors of the Eastern Han Dynasty, later Tang Emperors only exercised as much power as they could convince local warlords and wealthy aristocrats to give them.
Another key weakness had been growing for a long time. China still remained fundamentally dynamic, but life for common citizens had become harder under the Tang as wealthy landowners increased their holdings forcing small independent farmers to become poorly paid farm laborers and this trend worsened significantly after 755 AD. When the Tang fell in 907 AD only 50 years of political collapse followed. In 960 AD, Zhao Kuangyin reunified China and established the Song Dynasty. He reigned in Chinese expansionism and defined China as a nation. The Song boasted an economy so dynamic that it developed the world's first paper currency to prevent economic stagnation for want of hard currency. And it saw the urbanization and rise of the middle class which would also characterize the Renaissance in later European history.