Korean is the official language of South Korea and North Korea as well as one of the two official languages in China's Yanbian Korean Autonomous Prefecture. Approximately 78 million people speak Korean worldwide. For over a millennium, Korean was written with adapted Chinese characters called hanja, complemented by phonetic systems like hyangchal, gugyeol, and idu. In the 15th century, a national writing system called hangul was commissioned by Sejong the Great, but it only came into widespread use in the 20th century, because of the yangban aristocracy's preference for hanja. Most historical linguists classify Korean as a language isolate while a few consider it to be in the controversial Altaic language family. The Korean language is agglutinative in its morphology and SOV in its syntax.