 From 1948 to 1950, Han studied kwon bup, which was a mixture of Chinese chuan fa methods and Shudokan karate, and earned a black belt in the art under Byung In Yoon.Yoon's teachings later led to the development of one of the Korean schools of kong soo do and greatly influenced two of the early schools who helped to form modern taekwondo, the chang moo kwan and the jido kwan.At the outbreak of the Korean War, all martial arts schools in Korea were closed.