The demilitarized zone is also known as the joint security area or the 38th parallel and was established after the Korean War ended in an armistice in 1953 but technically North Korea and South Korea are still at war with one another. The 38th parallel was actually first proposed by the Japanese empire to the Russian empire to divide Korea into two parts in 1896 but no actual agreement was reached.
I visited the Panmunjon checkpoint in May, which is open to visitors under the supervision of United Nations troops, which are mostly American soldiers who are still stationed there after the Cold War. The whole demilitarized zone is said to have one million troops guarding it from both the North and the South. The thing that was most impressive was the fact that it was absolutely quiet within the area and also that one feels unexpectedly safe there.