After World War II and the Japanese defeat, the Japanese occupation left Korea. USA and the USSR split up Korea to be managed by the two super powers, the USSR in the north and USA in the south, to be later unified in a single election. However, as relations between the two grew worse with the progression of the Cold War, the 38th parallel division became more and more permanent. Eventually, Communist and Moscow-trained Kim Il-Sung became leader for the Democratic's People of Republic of Korea and the USSR troops departed.
Russia
China and the USSR
North Korea, South Korea, United States, and the USSR
South Korea, US vs North Korea, USSR, China
because ussr forced north korea to be communist by army
North Korea was supported by the USSR and China and was opposed by the United Nations Forces including South Korea.
To North Koreans kinda but the Koreans can't be trusted with what Kim Jomg Il has done to his people.(Kim Jong Il is basically the owner of North Korea.)
USSR/Red China supplying both NORTH Korea & NORTH Vietnam during both of those wars. Communists: USSR/Red China/North Korea/North Vietnam.
Result: the USSR got to test out their new equipment. Without Soviet supplies, North Korea would've had no tanks, artillery, jets, fuel, or ammo. Without the USSR, there would have been no Korean War.
They are run by two different types of government, and that of South Korea feels threatened by that of the North for that reason.
After Korea became independent after Japan in 1945, Korea didn't have unified government. US military controlled South and USSR controlled North.
Japan annexed Korea and had control of it until it lost WWII and the Allied Powers USSR occupied the North and USA occupied the south.