When North Korea invaded South Korea to make the entire peninsula communist, the war began
38th Parallel
The United Nations sent troops to South Korea to push back North Koreas troops from South Korea into China. The United States and South Korea were on the democratic side, while North Korea, China, and Soviet Union were communist.
Ceasefire/End
When the North Korean troops were pushed into China, China, who was communist, retaliated by sending their army to help the North Korean troops and push back the democratic side.
Division Today
DMZ
The 38th Parallel was the dividing line between North and South Korea. The United Nations troops pushed the North Korean troops past this line. It is where the DMZ would be made.
The war continued for a while, in which North Korea would attack South Korea and the U.N. army would defend and retaliate. President Truman did not want to appear weak, so he didn't sign a peace treaty, but when Eisenhower became president, he signed a treaty on July 17, 1953.
The treaty ended the war and now North and South Korea are divided by the border known as the DMZ, a two mile long border at the 38th parallel. The DMZ stands for the demilitarized zone.