Two young American officers, Dean Rusk and Charles Bonesteel, picked the line that still divides Korea: on 10 August 1945, working against the clock with a National Geographic map, they chose the 38th parallel because it cut the peninsula roughly in half while keeping Seoul in the American zone. Korea, a Japanese colony since 1910, was split on 2 September 1945 into a Soviet occupation zone in the north and a US zone in the south. Each zone formed its own state in 1948, the Republic of Korea in Seoul and the Democratic People’s Republic of Korea in Pyongyang, and the Korean War of 1950–1953 ended not in a peace treaty but in the armistice of 27 July 1953, signed at Panmunjom. The border since then has been the Military Demarcation Line, running through a Demilitarized Zone (DMZ) about 250 km long and 4 km wide that crosses the 38th parallel at an angle. North Korea covers 120,540 km² and has about 26 million people; South Korea covers roughly 100,000 km² and has about 52 million.
The 38th Parallel: A Line Chosen in Washington, August 1945
The Allies had already agreed that Korea should be freed from Japan. At the Cairo Conference in November 1943, Franklin D. Roosevelt, Winston Churchill and Chiang Kai-shek declared that Korea would “in due course” become free and independent, and Roosevelt floated a period of international trusteeship. The Soviet Union declared war on Japan on 8 August 1945 and its troops advanced quickly into the north of the peninsula. Fearing they might occupy all of it, Washington asked Rusk and Bonesteel to define an American zone. No Korea experts were consulted. Neither officer knew that Japan and imperial Russia had discussed sharing Korea along the same parallel about forty years earlier, and Rusk later said that if he had known Korean history he would almost surely have picked a different line.
Moscow accepted the proposal, and it went into General Order No. 1 for the Japanese surrender. The line put about 16 million Koreans in the American zone and 9 million in the Soviet one. It was meant to be temporary. In December 1945 the Moscow Conference of Foreign Ministers agreed on a five-year, four-power trusteeship, but many Koreans opposed it, and two years of US–Soviet talks on putting it into effect broke down as the Cold War deepened.
Seoul, Pyongyang and Kaesong: Two States, Then War Across the Line
The United States passed the Korean question to the United Nations. When the Soviet Union rejected the UN’s plan, UN-supervised elections were held in 1948 in the south only, and Syngman Rhee became president of the Republic of Korea, proclaimed in Seoul on 15 August 1948. In the north, Kim Il Sung consolidated power, and the Democratic People’s Republic of Korea was proclaimed in Pyongyang on 9 September 1948. Each government claimed to be the only legitimate authority over the whole peninsula.
The 38th parallel quickly became a front. Both sides fought border clashes, and Rhee’s government suppressed communist uprisings on Jeju island and at Yeosu and Suncheon. Moscow had at first been willing to consider only a limited operation on the Ongjin Peninsula on the west coast, but on 21 June 1950 Kim revised his plan into a general attack across the parallel, and North Korean forces invaded on 25 June 1950. Kaesong, the ancient capital of the Goryeo kingdom, had been under American and then South Korean control since 1945 and was captured by the North. Seoul was captured on 28 June. With the Soviet delegate absent, the UN Security Council condemned the invasion, and forces from 21 countries eventually served under the UN Command, with the United States providing about 90% of the personnel.
Busan, Incheon and the Yalu: The Front Sweeps the Peninsula
By early August 1950 the South Korean army and its allies held only a corner in the south-east. The Pusan Perimeter was a defensive line about 230 km long around the port of Busan, defended from 4 August to 18 September 1950 by around 140,000 UN troops against about 98,000 North Korean soldiers, with heavy fighting around Taegu (Daegu), Masan, Pohang and along the Naktong River. Busan and Daegu were the only two South Korean cities the North did not capture in the first three months of the war. Busan became the de facto capital of South Korea, and around 500,000 refugees were living there in early 1951.
On 15 September 1950 General Douglas MacArthur turned the war with a landing at Incheon, the port for Seoul far behind the front line, involving some 75,000 troops and 261 naval vessels. Seoul was recaptured about two weeks later, and UN forces broke out of the perimeter on 18 September. They crossed the 38th parallel in October, captured Pyongyang on 19 October, and pressed on towards the Yalu River, the border with China.
On 19 October the Chinese People’s Volunteer Army crossed the Yalu. In the frozen mountains of the north-east, about 120,000 Chinese troops encircled some 30,000 UN soldiers at the Chosin Reservoir between 27 November and 13 December 1950, and the UN forces fought their way out to the port of Hungnam for evacuation by sea. UN forces retreated from North Korea in December. Communist forces took Seoul again in January 1951 and lost it to a UN counter-offensive two months later. After a failed Chinese spring offensive, the front settled close to where the war had begun, near the 38th parallel, and turned into a war of attrition while armistice talks dragged on for two years.
Panmunjom and the DMZ: The Line Fixed in 1953
Talks opened in Kaesong on 10 July 1951 and moved on 25 October 1951 to Panmunjom, a cluster of fewer than ten huts on the Kaesong–Seoul road, about 53 km north-north-west of Seoul and 10 km east of Kaesong. The armistice was signed there on 27 July 1953 by US Lieutenant General William Harrison Jr. and General Mark W. Clark for the UN Command, Kim Il Sung and General Nam Il for the Korean People’s Army, and Peng Dehuai for the Chinese volunteers. South Korea never signed, because Rhee refused to accept a divided country. No peace treaty has followed, so the two Koreas remain technically at war.
The armistice fixed the new border along the final front line, not the 1945 parallel. The Military Demarcation Line runs about 248 km across the peninsula, with a strip 2 km deep on either side forming the DMZ. In the west the line lies south of the 38th parallel and in the east north of it, so the North gained ground around Kaesong and the South gained mountains in the east. Kaesong, the site of the first armistice talks, lay in pre-war South Korea but is now part of North Korea. The war caused around one million military deaths and an estimated 1.5 to 3 million civilian deaths.
The Joint Security Area at Panmunjom, its blue huts straddling the demarcation line, is the only place where soldiers of the two Koreas stand face to face. It is where prisoners of war were exchanged across the Bridge of No Return in 1953, and where Kim Jong Un and Moon Jae-in adopted the Panmunjom Declaration in the Peace House on the southern side on 27 April 2018, pledging to work towards formally ending the war. Later that year the two sides agreed to clear the Joint Security Area of landmines, weapons and guard posts, a withdrawal completed on 25 October 2018, leaving 35 unarmed security guards. Our guide to what the Korean DMZ is looks at the zone itself in more detail.
Yeonpyeong, Kaesong and Imjingak: The Division Today
At sea the armistice drew no boundary. The Northern Limit Line in the Yellow Sea is widely believed to have been set by the UN Command on 30 August 1953, although no original documentation has been found, and North Korea disputes it. It leaves islands such as Yeonpyeong and Baengnyeong in South Korean hands although they sit just off the North Korean coast, and the waters around them have seen repeated clashes. On 23 November 2010 North Korean forces fired around 170 artillery shells and rockets at Yeonpyeong, killing both soldiers and civilians.
Kaesong itself became the main experiment in cooperation. The Kaesong Industrial Region, about 10 km north of the DMZ and an hour’s drive from Seoul, ran from 2004 to 2016 as a joint project in which South Korean firms employed North Korean workers. By April 2013, 123 South Korean companies employed about 53,000 North Korean workers there, but Seoul closed the park on 10 February 2016 and recalled its staff.
On the South Korean bank of the Imjin River near Paju, Imjingak park was built in 1972 for people unable to return to homes and families on the other side of the line, and it receives about 1.2 million visitors a year. Its Freedom Bridge, a former railway bridge, carried prisoners of war returning from the North. The division also defines North Korea’s other frontiers, which follow the Yalu and Tumen rivers and are mapped in the guide to the countries that border North Korea. Seventy years on, the peninsula is still waiting for the kind of settlement Germans reached in the peaceful reunification of Germany in 1990.