Korean (한국어/조선말, see below) is the official language of South Korea and North Korea, as well as one of the two official languages inChina's Yanbian Korean Autonomous Prefecture. About 80 million people speak Korean worldwide. For over a millennium, Koreans wrote with adapted Chinese characters called hanja, complemented by phonetic systems like hyangchal, gugyeol, and idu. In the 15th century,Sejong the Great commissioned a national writing system called Hangul, but it only came into widespread use in the 20th century, because of the yangban aristocracy's preference for hanja. Classification The majority of historical linguists classify Korean as a language isolate. There are still a small number who think that Korean might be related to the putative Altaic language grouping, but linguists agree today that typological resemblances cannot be used to prove genetic relatedness of languages as these features are typologically connected and easily borrowed. Such factors of typological divergence as Middle Mongolian's exhibition of gender agreement can be used to argue that a genetic relationship is unlikely. History Korean is descended from Proto-Korean, Old Korean, Middle Korean, and Modern Korean. Since the Korean War, contemporary North–South differences have developed in standard Korean, including variance in pronunciation, verb inflection, and vocabulary. Official status Korean is the official language of South Korea and North Korea. It is also one of the two official languages of the Yanbian Korean Autonomous Prefecture in China. In South Korea, the regulatory body for Korean is the Seoul-based National Institute of the Korean Language (국립국어원; 國立國語院), which was created by presidential decree on January 23, 1991. In North Korea, the regulatory body is the Language Institute of the Academy of Social Sciences (사회과학원 어학연구소; 社會科學院語學研究所, Sahoe Kwahagwon Ŏhak Yŏnguso).