However, Western historians and linguists have put forward their suggestions on about the origin of the Japanese language. The major was the so-called "northern" and "South" theory. Proponents of the theory first argued that Japanese is akin to Altaic languages, and supporters of the second theory tended to Austronesian origins of language. After the end of the Sino-Japanese War (1937-1945 years), scientists of the two countries engaged in the history of the origin of Korean and Japanese languages, analyzing ancient folklore texts, discovered a number of phonetic patterns that pointed to the fact that languages are closely related. Having considered the materials of the ancient languages on the Korean Peninsula, the researchers found that naiblizhayshim akin Japanese language is existing in the state of Koguryo and tribal union Karak (or Kai) language. So, if we consider the language and structure of words and language drevneyaponskogo kayaskogo and Koguryo language, we can see very many similarities. In the ancient chronicles highlighted the fact that Japan has maintained close contact with Baekje, Baekje and language, in addition to that included elements of the Koguryo language, and still had family connections with the ancient Chinese language. Japanese Korean shaped by a long time.

So, along with the fact that there were differences between the inhabitants of the Ryukyu Islands and the Japanese have taken place and ethnographic, anthropological and linguistic similarities. Approximately in the IV century AD, Japanese and ryukyusky languages were divided, and perhaps in this period, a group of settlers from the Korean peninsula from the northern Kyushu replaced some part local population. The result was the relocation of people to the south Ryukyu, and immigrants who are ancestors of the Japanese nation, as settled in Kyushu, Honshu and Shikoku, and the other adjacent to it smaller Islands. Referred to in historical documents that confirm that the intermediate between the West and ryukyuskim Japanese language is a dialect kyusyuysky. The inhabitants of the islands of Japan and many tribes displaced century were in close contact with each other.

And the fact that there were links between the language of Paekche, the language of Karak and the language of Koguryo is undeniable. Based on this and all of the above we can conclude that Japanese is akin to a group drevnekoreyskih languages, also known as pueskaya group. During the transition to self-imposed isolation of Japan in political terms, the further development of language influence the language of those tribes which migrated to Japan during the Kofun and Yayoi. These tribes were related to Koreans, which has led to borrowing of vocabulary avstraloneziyskogo language, as well as to simplify the Japanese language through the transformation of its phonetics.