> But we rarely think about ethnic imperialism — an empire trying to gobble up neighboring polities because of linguistic and cultural similarity, so that it can be the ruler of a specific cultural sphere. (In fact, the British conquest of Ireland, the Japanese conquest of Korea and China)

Uh no. The Yamato people wanted these countries for land and resources. Japan was never interested in extending their culture, nor proactively assimilating other ethnic groups into their own, with the exception of maybe the Ryukyuan on Okinawa. If this were the case, you’d seen it in Taiwan. They didn’t want to assimilate the Koreans who already in their country for generations, either. I can only presume author is a white person, because the cultural affinity of Japan bifurcated from China a millennial ago. Speaking of which, the other motivation was to prevent and buffer Japan from being controlled and humiliated by a white colonizers, as was the case with China.