2 Answers

You have a misconception of events, North Korea did not split from South Korea or vis versa

Japan invaded China and Korea in the thirties.  Japanese occupation of Korea ended after World War II in 1945. At the time Korea was occupied by the Soviet Union north of the 38th parallel and by the United States south of the 38th parallel.

The United States suppressed an existing network of local Peoples Committees; meanwhile Cold War tensions rose. This led in 1948 to the establishment of two governments claiming to be the sole government of all of Korea: a communist North, and a United States-controlled South, led by anti-communist Syngman Rhee.

In 1950 North Korea invaded South Korea, starting the Korean war.  After the armistice was signed both countries returned the original border on the 38th parallel

Technically North and South Korea are still in a state of war.

Kim jong was mad because he has no "Seoul".....