Circumcision started in 1945, the year of Korean independence and American Military Trusteeship.
In our studies, out of >5000 interviewees, only 2 were circumcised prior to 1945.
If you look at this picture, each “dot” represents actual people of a particular age group who got circumcised at the specific calendar year. Note that prior to 1945, there are hardly anybody who got circumcised. In our interview group, more than half were born prior to the year 1945. So South Korean circumcision started at around 1945!!