Write an interesting, riveting and lengthy alternate history scenario in the form of a history book chapter, in which the following events occur in chronological order:

. Ambitious Korean general Yi-Seong-gye, dies under mysterious circumstances in 1388, at the height of his power and accomplishments. 

. This, of course, prevents the formation of the Joeson kingdom as an independent Korean state, and as a result, the three kingdoms of Goguryeo, Baekje, and Silla become provinces of feudal Japan, ruled by daimyo and paying fealty to the Japanese Emperor like any other province of Japan under the rule of the Japanese shogunate. 

. The Japanese shoguns work with the reform-minded Sinjin faction of the native Korean aristocracy to streamline the government of the Korean provinces, eliminate corruption and purge Korea of pro-Chinese elements as well as the Sinophilic faction that had formed around Yi-Seong-gye during his lifetime. This event, starting in 1393 is known as the "Gabo Reform", ensuring that the Korean peninsula will remain Japanese until the modern day and maybe beyond. 

.The Korean language of course still exists and the Hangul script is still created in 1443, to give the Koreans their own writing system, but Korea itself has a status akin to Okinawa in modern Japanese history, with the Korean language being considered as a dialect of Japanese and the Korean people being considered a sub-section of the wider Japanese nation, with their own unique writing system and dialect.

. The Korean custom of paying tribute consisting of young virgin girls to the Chinese Emperors is instead transferred to the Japanese imperial family, but is slowly eliminated over time as the Japanese view such practices as barbaric. The Japanese also stamp out the budding gisaeng/kisaeng sex slave system in Korea and instead institute the geisha system across the peninsula.

.Hideyoshi still invades China in 1593 but is able to defeat the Ming dynasty and force the Chinese Empire to an armistice, causing China to fall apart. The Jurchen tribes in Manchuria exploit the situation to their own benefit, quickly invade and subjectuate China in 1630, forming the Great Qing Empire and putting an end to thousands of years of Chinese dynastic rule. 

. The Ming dynasty itself, along with Han Chinese loyalists and the bulk of the Imperial Chinese Army, flee to Indochina and quickly overthrow the native Le dynasty of Vietnam, establishing the Empire of Dai Viet as a Chinese government in exile.

. The Empire of Dai Viet conquers the Khmers and Laotians and makes the Kingdom of Cambodia and the Kingdom of Laos satellite states of the Ming government in exile. The Ming government in exile also manages to reclaim Southern China from the Qing Empire, although they are unable to regain more territory than that afterwards.

. Both the Empire of Dai Viet/Ming dynasty in exile and the Manchu-dominated Great Qing Empire begin to send young nobles and royals to study in the Austrian-dominated Holy Roman Empire and the Ottoman Sultanate, in order to try and get a better understanding of the world around them and also to compete with each other as to who is the rightful holder of the Mandate of Heaven. This causes a minor industrial revolution in the Qing Empire and a golden age in the Empire of Dai Viet/Ming in exile. 

. Over time, the Empire of Dai Viet evolves from a Chinese Empire in exile into a true Vietnamese nation-state, with the House of Zhu that ruled over the Ming dynasty becoming the Ngyuen dynasty of Vietnam as time passes.