Sui dynasty
Foundation and Emperor Wen

During the late Northern and Southern dynasties period, the Xianbei -ruled Northern Zhou conquered the Northern Qi in 577, reunifying northern China. By this time, Yang Jian, a Northern Zhou general who would later found the Sui dynasty, became the regent to the Northern Zhou court. Yang Jian's clan, the Yang clan of Hongnong, had Han origins and claimed descent from the Han dynasty general Yang Zhen, but had intermarried with the Xianbei for generations. Yang Jian's daughter was the Empress Dowager, and her stepson, Emperor Jing of Northern Zhou, was a child. After crushing an army in the eastern provinces, Yang Jian usurped the throne from the Northern Zhou rulers, and became Emperor Wen of Sui. While formerly the Duke of Sui when serving at the Zhou court, where the character 隨 literally means 'to follow', implying loyalty, Emperor Wen created a unique character 隋, morphed from that in his former title, as the name of his new dynasty. In a bloody purge, Wen had 59 Zhou princes eliminated, in contrast to his later reputation as the "Cultured Emperor". Emperor Wen emphasized Han cultural identity during his reign, abolishing the anti-Han policies of Northern Zhou and reclaiming his Han surname of Yang. Having won the support of Confucian scholars who held power in previous Han dynasties (abandoning the nepotism and corruption of the nine-rank system), Emperor Wen initiated a series of reforms aimed at strengthening his empire for the wars that would reunify China.

In his campaign for southern conquest, Emperor Wen assembled thousands of boats to confront the naval forces of the Chen dynasty on the Yangtze River. The largest of these ships were very tall, having five layered decks and the capacity for 800 non-crew personnel. They were outfitted with six 50-foot-long booms that were used to swing and damage enemy ships, or to pin them down so that Sui marine troops could use act-and-board techniques. Besides employing Xianbei and other Chinese ethnic groups for the fight against Chen, Emperor Wen also employed the service of people from southeastern Sichuan, which Sui had recently conquered.

In 588, the Sui had amassed 518,000 troops along the northern bank of the Yangtze River, stretching from Sichuan to the East China Sea. The Chen dynasty could not withstand such an assault. By 589, Sui troops entered Jiankang (now Nanjing) and the last emperor of Chen surrendered. The city was razed to the ground, while Sui troops escorted Chen nobles back north, where the northern aristocrats became fascinated with everything the south had to provide culturally and intellectually.

Although Emperor Wen was famous for bankrupting the state treasury with warfare and construction projects, he made many improvements to infrastructure during his early reign. He established granaries as sources of food and as a means to regulate market prices from the taxation of crops, much like the earlier Han dynasty. The large agricultural surplus supported rapid growth of population to a historical peak, which was only surpassed at the zenith of the Tang dynasty more than a century later.

The capital of Daxing (Chang'an, modern Xi'an), while situated in the militarily secure heartland of Guanzhong, was remote from the economic centres to the east and south of the empire. Emperor Wen initiated the construction of the Grand Canal, with completion of the first (and the shortest) route that directly linked Chang'an to the Yellow River (Huang He). Later, Emperor Yang enormously enlarged the scale of the Grand Canal construction.

Externally, the emerging Turkic Khaganate in the north posed a major threat to the newly founded dynasty. With Emperor Wen's diplomatic manoeuvre, the Khaganate split into Eastern and Western halves. Later the Great Wall was consolidated to further secure the northern territory. In Emperor Wen's late years, the first war with Goguryeo, ended with defeat. Nevertheless, the celebrated "Reign of Kaihuang" (era name of Emperor Wen) was considered by historians as one of the apexes in the two millennium imperial period of Chinese history.

The Sui emperors were from the northwest military aristocracy, and they cited as their ancestors the Yang of Hongnong 弘農楊氏, a Han clan. They emphasised their Han ancestry, and claimed descent from the Han official Yang Zhen. The New Book of Tang traces their patrilineal ancestry to the Zhou dynasty kings via the Dukes of Jin. The Li of Zhaojun and the Lu of Fanyang hailed from Shandong and were related to the Liu clan, which was also linked to the Yang of Hongnong and other clans of Guanlong.

The Yang of Hongnong, Jia of Hedong, Xiang of Henei, and Wang of Taiyuan from the Tang dynasty were later claimed as ancestors by Song dynasty lineages. Information about these major political events in China were somehow filtered west and reached the Byzantine Empire, the continuation of the Roman Empire in the east. From Turkic peoples of Central Asia the Eastern Romans derived a new name for China after the older Sinae and Serica: Taugast (Old Turkic: Tabghach), during its Northern Wei (386–535) period. The 7th-century Byzantine historian Theophylact Simocatta wrote a generally accurate depiction of the reunification of China by Emperor Wen of the Sui dynasty, with the conquest of the rival Chen dynasty in southern China. Simocatta correctly placed these events within the reign period of Byzantine ruler Maurice. Simocatta also provided cursory information about the geography of China, its division by the Yangzi River and its capital Khubdan (from Old Turkic Khumdan, i.e. Chang'an) along with its customs and culture, deeming its people " idolatrous " but wise in governance. He noted that the ruler was named "Taisson", which he claimed meant "Son of God", perhaps Chinese Tianzi (Son of Heaven) or even the name of the contemporary ruler Emperor Taizong of Tang.
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