1) The Korean Peninsula was divided after World War 2 along the 38th parallel, with the North occupied by the Soviet Union and the South occupied by the United States. This division led to the establishment of North and South Korea as separate states in 1948.
2) The Korean War broke out in 1950 when North Korea invaded South Korea, leading to United Nations involvement headed by the United States on South Korea's side and Chinese involvement backing North Korea.
3) The Korean War ended in 1953 with an armistice and demilitarized zone established along the border between North and South Korea, dividing the peninsula and leaving the two Koreas still in a state of conflict.