Hi AskHistorians, My question to you is how come the South Koreans and North Koreans have a language barrier despite only splitting 75 years ago. The writing and the speech is sometimes unrecognizable to either side which surprised me a lot.
Was there always a difference between the Northern and Southern tounge or did the division cause this shift?
The difference is mainly due to pre-existing dialects. There are 7 major groups of Korean dialects: a central dialect used on both sides of the North-South border, 3 southern dialects (SE, SW, and Jeju), and 3 northern dialects (NE, NW, and Central Asian). The SE, SW, NE, and NW dialects closely map to the northern and southern provinces, and are often named after them:
SE = Gyeongsang
SW = Jeolla
NE = Hamgyeong
NW = Pyeongan
and
Central dialect = Chungcheong, Gangwon, Gyeonggi and Hwanghae provinces
Jeju dialect = Jeju Island
Central Asia dialect = Kazakhstan and Uzbekistan
Korean languages were only standardised after independence, and thus after the division into North and South - it was not politically possible during the Japanese colonial period. In South Korea, Standard Korean is based on the Seoul dialect (= the Gyeonggi version of the central dialects); it is closely related to the pre-colonial de facto standard Korean. In North Korea, Standard Korean is in principle based on the Pyongyan version of the NW dialect, but in practice is a mix of central and NW dialects. Korean speakers in Manchuria mostly speak versions of the NE dialect, and the Central Asia dialects could be (and often are) considered members of the NE dialects. The are significant differences between the NE and Central Asian dialects, due to being separated for about 100 years, the split being before most of the modernisation of Korea.
Essentially, the differences between Standard Korean in North Korea and South Korea is because they started from different dialects. Also, North Korea resists the use of English loanwords. That they are so similar is due to both being at least partly based on central dialects.
Jeju dialect is not mutually intelligible with the mainland dialects, and is sometimes classified as a separate language rather than as a dialect. This lack of mutual intelligibility is nothing new - it's been that way for at least 500 years.
Further reading:
Jaehoon Yeon, "Korean dialects: a general survey", chapter 6 in Nicolas Tranter (ed), The Languages of Japan and Korea, Routledge, 2012.
