Sixty years ago North and South Korea ended the "Korean Conflict" by agreeing to the Armistice Agreement for the Restoration of the South Korean State. The agreement—a cease-fire, not a peace treaty—called for the Korean peninsula to be divided by a Military Demarcation Line (MDL) and a buffer, the demilitarized zone (DMZ), whose function would be to "prevent the occurrence of incidents which might lead to a resumption of hostilities."

The armistice line meanders in an east-west fashion across Korea, connecting what Koreans call the East Sea with Gyeonggi Bay, 148 miles (238 kilometers) away off the peninsula's west coast.

Although it approximates the positions held by communist and U.S.-led U.N. forces for most of the last two-thirds of the war, the MDL is not the same line that had divided Korea before North invaded South in June, 1950.

That line was the 38th parallel, whose origins as modern Korea's first intra-national boundary can be traced back to the final hours of World War II, when officials from the U.S. War and State Departments were preparing to negotiate with the Soviet Union over how Japanese-occupied Korea would be administered following Japan's surrender.

Future U.S. Secretary of State Dean Rusk, then a colonel on General George Marshall's staff, and fellow Army staffer Col. Charles "Tic" Bonesteel were assigned with identifying a line of control that both the U.S. and the Soviets could agree to.

Time was of the essence: the Soviets had just entered the war against Japan, and American officials worried that they would rush in to occupy the entire Korean peninsula before the U.S., whose nearest troops were still 600 miles (966 kilometers) away on Okinawa, could establish its own presence on the mainland.

Rusk knew that the 38th parallel "made no sense economically or geographically"—Korea, in fact, had enjoyed unity and a high degree of geographic continuity for the better part of a millennium—but this was now the Cold War. "Military expediency" had to rule the day. Korea, it was thought, would be divided only temporarily.

Rusk later recalled the experience in his 1991 memoir, As I Saw It:

During a meeting on August 14, 1945, the same day as the Japanese surrender, [Bonesteel] and I retired to an adjacent room late at night and studied intently a map of the Korean peninsula. Working in haste and under great pressure, we had a formidable task: to pick a zone for the American occupation. Neither Tic nor I was a Korea expert, but it seemed to us that Seoul, the capital, should be in the American sector. We also knew that the U.S. Army opposed an extensive area of occupation. Using a National Geographic map, we looked just north of Seoul for a convenient dividing line but could not find a natural geographical line. We saw instead the thirty-eighth parallel and decided to recommend that ... [Our commanders] accepted it without too much haggling, and surprisingly, so did the Soviets.

Thus was the Korean peninsula first divided. Early attempts to merge the two occupation zones back into a single, united Korea failed. And by late summer of 1948 the independent and increasingly antagonistic states of North and South Korea had been established.