Write an interesting, riveting, lengthy alternate history scenario in the form of a history book chapter, in which the 'barbarians' who conquer the Ming dynasty in 1644 and subsequently put an end to thousands of years of Chinese dynastic traditions, are not the Jurchen tribes of Manchuria, but instead, the well-trained and professional armies of the Tokugawa shogunate of feudal Japan, who had earlier on conquered Korea and liberated the peninsula from the Joeson Kingdom ruled by the Yi dynasty as its royal family during the Imjin War of 1592-1598, before marching on to Beijing and Nanking/Nanjing from Korea and forcing the Ming dynasty to agree to a humiliating armistice that recognizes Japanese control over Korea, as well as making the Joeson Kingdom a illegitimate state. The reason for the Japanese conquest of China is to solidify Japan's spot as the dominant power in East Asia and also so that the Japanese Imperial Family can claim the Mandate of Heaven, from the now-crumbling Ming dynasty The brave warriors of the Ming dynasty fight bravely against the invading Japanese forces, but the once-mighty Ming dynasty is on the verge of collapse and in just a year's time, the Japanese conquer China with the help of their old Mongol allies and the Manchurian tribes and re-establish the Tang Empire, which had been dissolved in 908. A series of military expeditions to secure the borders of the restored state and establish dominance see the conquest of Taiwan, East Turkestan and Tibet, with the descendants of the House of Zhu, the ruling family of the Ming dynasty, fleeing to Vietnam along with their loyalists and remnants of the Imperial Chinese Army, where they overthrow the native Tây Sơn triều [Tây Sơn dynasty] of Vietnam in 1802 and establish the Đại Việt quốc [Empire of Vietnam] or Nam Triều [Southern dynasty] as a simultaneous continuation and restoration of the Ming rump state Nán Míng [Southern Ming], which had been conquered by the Japanese in 1662. However, the Đại Việt quốc's emperor Gia Long decides to submit to the Japanese and makes Vietnam a tributary state of the Tang, in exchange for Vietnam receiving the core territories of China under the Ming and Gia Long's family marrying into the descendants of the House of Zhu who remained in China after the Ming conquest, to prevent revolt in China.