Korea Goguryeo conquers Japan

[Sarrugi lugal]

Goguryeo lose their domains north of yalu river to China
They focus on south and unite Korea
Before Yamato begins
Japan is conquered by them and Koreanized with mass settlement

How would this effect East Asian and world history ?

 

[Beanstalk]

This is mostly ASB. Goguryeo was originally founded north of the Yalu River.
It is more likely to follow the course of the Jin Dynasty or the Qing Dynasty than to invade across the sea.
Nevertheless, if Goguryeo managed to conquer Japan, the culture of Japan and Korea would have completely changed.

This is because Silla, the source of modern Korea, was also defeated in order to conquer Japan.
Goguryeo was close to Jurchen.