The Japanese dominated southern peninsula was captured by the USA while the northern peninsula above the 38th parallel was taken by Russia. Russia, I remind, was an ally in that war. Russia had a right to it's sovereignty and it's portion of peacekeeping.
The southern peninsula was seen by the USA as a threat no different than Japan and after the two nuclear weapons dropped on Japan it came to be understood the USA would possess most of the strongholds of Japan.
Hence.
The great Korean divide.
Guess what?
Communism came to be the government of choice in the North while the South found it's incorporation of 'Democracy American Style' dominating it's society. Well. I'll be darn.
No magic here boys and girls. No evil. No 'Axis of Evil.' Simply history as it played out post WW II.
The 'story' is summerized like this:
South Korea was invaded by North Korea on June 25th, 1950. The United Nations sent military assistance. The Korean War lasted three years and inflicted terrible damage to Korea before a cease-fire ended the war in 1953. The 4 kilometer-wide area along the Military Demarcation Line which divides North and South Korea has become known as the DMZ, or Demilitarized Zone. Over the 52 years since the Korean War there have been continual conflicts along the DMZ.
South Korea continues in its efforts to unify North and South Korea.