After World War II ended, Korea was split into two parts: North Korea and South Korea. The Korean War involves North Korea/China and South Korea/United States. The war went back and forth from North Korean territory and South Korea territory as shown in the picture.On June 6, 1950, North Korea crossed the 38th parallel and invaded South Korea, starting the 3-year war called the Korean War. In three days, the North Korean forces captured South Korea's captial city, Seoul. They continued to advance farther down South Korea around the Pussan Perimeter and fought there. Because General McArthur had cut North Korea's supplies, the North Korean army had to retreat. In doing so, the UN forces then crossed the 38th parallel into North Korea. However, in December 1950, the Chinese joined the NK forces and pushed back SK forces back to Seoul. On April 11, 1951, President Truman dismissed General McArthur for challenging his authority as general. Afterwards, however, the UN forces were able to push back the Chinese and NK forces to the original border. After two more years of war, they finally came to a conclusion of establishing the 38th parallel as their permanent borderline, or the DMZ. The Korean War was a battle between North and South Korea and was what truly separated the them from each other.
For more info, go to history.com
For more info, go to history.com