This study aims to show that language purification policies are the most important factors that influence Korean language differentiation, based on the premise that Korean is a pluricentric language having two regional varieties: South Korean P’yojuno and North Korean Munhwao. To this end, on the basis of a precedent study that analyzed regional variation mechanisms in French through four factors—terminological, socio-terminological, psycho-terminological, and extra-terminological—we identified two factors having great influence on the language change in South and North Korean societies: socio-terminological and extra-terminological. We also found that these factors precisely correspond to two categories in Kloss's(1969) theory of language planning— corpus planning and status planning; this confirmed that we should consider Korean language differentiation from the standpoint of language policy. There are many factors that cause language differentiation, and there is no doubt that these factors also have complex interrelationships. However, this study is all the more meaningful in that it uses systematic analysis to state that language policy plays an important role in Korean language differentiation.