Complex sentence: From 1906 ~ 1945, they changed the school name several times and when the school name was Gyeseong nation school, it was closed for a while because of the 6.25 Korean War and reopened at 1964 March.
Split into simpler sentences: From 1906 ~ 1945, they changed the school name several times. When the school name was Gyeseong nation school, it was closed for a while because of the 6.25 Korean War and reopened at 1964 March.