Chinese Imperial Restoration: The Sui (581–618) and Tang (618–907) Dynasties
The Sui Reunification (589) and the Founding of the Tang
In 581, a palace coup brought a new dynasty, called Sui, to power in the history-haunted region “Within the Passes” in northwest China. The founder of this dynasty was a man named Yang Jian (541–604). As emperor, he is known as Sui Wendi (the “Cultured Emperor of the Sui”). His father had been a high official, ennobled as the Duke of Sui, under the last Xianbei-ruled regime in northwest China (the Northern Zhou Dynasty). Yang Jian inherited his father's title as Duke of Sui, and his daughter was selected to be a consort for the imperial crown prince. When this crown prince, in due course, inherited the throne in 578, it made Yang Jian the father-in-law of the reigning emperor – always a potentially influential position. Because this emperor only lived two more years and was succeeded by a young boy, Yang Jian was then well placed to step in and grab supreme power for himself. After eliminating all potential legitimate heirs to the throne, and quelling a certain amount of armed opposition, Yang Jian usurped the throne outright, founding the Sui Dynasty.
A few years earlier, in 577, the last independent Xianbei-ruled dynasty in northeast China (the Northern Qi) had already been conquered by the predecessor of the Sui Dynasty in the northwest (that is, Northern Zhou), accomplishing the reunification of north China. The new Sui Dynasty now aspired to conquer the south too, and complete the reunification of a Chinese world that had been divided (with one brief exception) ever since the disintegration of the Han Dynasty that began in 184. The south, meanwhile, had never recovered from a devastating mid-century rebellion (548–552), which had severely diminished Southern dynasty imperial resources. In particular, control over the strategic upper (western) reaches of the Yangzi River had now passed from the south to the north. During the centuries of division, the north had frequently been able to field superior cavalry-based armies, but the south had always been protected, when all else failed, by the formidable natural barrier of the Yangzi River. Now the south was vulnerable to attack down the line of the river from the west. The final southern military defense also appears to have been ineptly led.