>>213884285
>the Gogureyo people push into the southern peninsula kingdoms like Gaya and Silla.
Just to clarify, Gogureyo is a Kingdom, its not an ethnicity. Gaya and Silla were created well after the Yayoi migration started.
The Korean peninsula was already well established by the time the Yayoi period and migration to Japan began. Its not like the people living in southern part of the peninsula were free ranging nobodies, they were Koreans living in the Jin state of Korea. They were all Korean.
The Koreans who left to Japan, starting with the Yayoi and through the Kofun periods, left because Korea was going through political instabilities as the Proto-Three Kingdoms period of Korea started and those three parties fighting for power over the peninsula.
The Jin were basically powerless so they were easy pickings by the more powerful Korean kingdoms thus they were eventually broken up and formed other smaller kingdoms before power structure settled down and formed Baekje, Silla, Ye, etc. This is why they fled to Japan during this period as they were getting caught up in a power grab. The Jin has a lot of artifiacts that were known to be found in Japan showing their migration from Korea to Japan.