The Gilder Lehrman Institute of American History Advanced Placement United States History Study Guide

Period 8: 1945-1980

The Korean War

The Korean War was three different conflicts from the perspective of the disparate groups who fought in it. For North and South Korea, the conflict was a civil war, a struggle with no possible compromise between two competing visions for Korea’s future. To the North was a coalition led by three dictators—Josef Stalin, Mao Zedong, and Kim Il-sung—devoted to creating a Communist Korea, a single-party state that controlled all economic assets and all aspects of the people’s lives. To the south, the Republic of Korea (ROK) had a Western-style constitution and Christian-capitalist orientation and the support of the United States and the United Nations. Within Asia the war was a regional conflict over the future security of two Chinas, one Communist and one Nationalist, and the containment of Japan, while for the United States and the Soviet Union, the war for Korea was a limited part of a post-1945 global competition for power.

For each member of the Communist coalition—the Chinese, Russians, and North Koreans—the war was one more step toward destroying Japanese imperialism on the mainland of Asia. Japan had defeated the Chinese in 1895 and the Russians in 1905, and then incorporated Korea into the Japanese empire in 1910. The Koreans had continued to struggle against Japan in China and Manchuria and in a series of uprisings and guerrilla raids within Korea until Japan’s defeat by the Allies in World War II.

With Soviet assistance, the Chinese Communists defeated the Chinese Nationalists between 1945 and 1950. In February 1950, the People’s Republic of China and the Soviet Union signed a comprehensive alliance to oppose any intervention by the Chinese Nationalists, the Japanese, and the Americans that might reverse the Chinese Revolution. The Russians had been excluded from the Allied occupation of Japan after World War II, and Stalin and Mao Zedong thought a new Japanese-American conspiracy was afoot to mount a counteroffensive against Asian Communism. The first theater of that war would be Korea.

The United States had recognized Korean independence in 1882 but did nothing to stop the annexation of Korea by the Japanese. Only a handful of Americans, either Christian missionaries or educators, knew very much about Korea at all, let along the Koreans’ struggles against Chinese and Japanese imperialism or of the growth of Christianity in Korea. Koreans suffered along with the Chinese and Japanese from Americans’ anti-Asian racial prejudices. Whenever the United States dealt with Korea as a foreign policy issue, it was always within the broader context of relations with Japan. The Koreans resented this approach and continue to do so.

After the Japanese surrender in August–September 1945, the United States under an agreement with the Soviet Union sent an expeditionary force of three US Army divisions to Korea to disarm and repatriate 400,000 Japanese soldiers and civilians. The Soviets had already invaded and occupied northern Korea in their August 1945 campaign against Japan in Manchuria. To limit conflict between the allies, the US and USSR agreed to divide Korea at the 38th Parallel as a temporary control measure. The Americans recognized that the division put two-thirds of the thirty million Koreans under US protection. The southern zone included Seoul and the Han River Valley, as well as much of mountainous Korea’s scarce arable land. The Soviets took over Korea’s industrial heartland, gold and coal mines, fertilizer and concrete plants, and hydroelectric power system. This division, intended to be temporary, destroyed Korea’s economic viability.

Overwhelmed by almost one million Korean refugees returning from Japan and its wrecked empire, the US Army Military Government in Korea (USAMGIK) and the State Department watched political events unfold with dismay. In the Soviet zone, the Red Army looted and expropriated everything of value. They defined all property as “Japanese” and had the assistance of a Communist Korean security force led by an anti-Japanese partisan, Kim Il-sung. By 1948, Kim Il-sung dominated a new Korean Communist party and the Korean People’s Army or KPA, created on the pretext of defending the Democratic People’s Republic of Korea (DPRK) from an American-South Korean-Japanese invasion.

In southern Korea, the USAMGIK faced growing nationalist hostility to a long occupation and a trusteeship approved at a US-USSR conference in Moscow in December 1945. There was no obvious successor regime in South Korea, the choices being too close to the Chinese Nationalists. The Americans also faced an internal revolutionary Communist movement, the South Korean Labor Party (SKLP).

From the Korean perspective, the war began in 1946 with a nationalist anti-foreign uprising against the American occupiers, the Autumn Harvest Rebellion. Conflict continued into 1947 with strikes and terrorist attacks and broke out into a national insurgency in 1948. This resistance, led by the SKLP, did not prevent UN-sponsored elections and the creation of the Republic of Korea (August 1948) under a returned exile nationalist leader, Syngman Rhee. To the Americans, the autocratic, messianic Rhee was the least objectionable option. He was anti-Japanese, anti-Chinese, anti-Communist, and even anti-American when it served his purposes. He was neither pro-democracy nor pro-human rights.

The Republic of Korea with the assistance of American weapons and advisors won the war of 1948–1950, a classic “people’s war of national liberation” like the civil wars in China and Indochina. The South Korean army and police fought 600 engagements with Communist guerrillas in the ROK’s four southern provinces and Cheju Island. The same forces fought 200 engagements with the North Korean security forces along the 38th Parallel. In this guerrilla war, 7,500 Korean security forces and at least 34,000 other Koreans died violent deaths before June 25, 1950. Kim Il-sung wanted to invade the ROK in 1949, but Josef Stalin demanded a stronger KPA and a Chinese Communist commitment to help Kim Il-sung. Kim and Stalin (with Mao Zedong’s weak assurance) decided an invasion in 1950 would succeed. They believed the Americans would not intervene or would be too late to save the Rhee government. The South Koreans did not have the aircraft, tanks, artillery, or enough trained troops to stop the North Korean army.

The US government under President Harry S. Truman did not make a unilateral commitment to defend South Korea from invasion but did pledge to protect the ROK through the United Nations. The Communists simply did not believe this pledge because the US had withdrawn its last combat units in 1949, which was one of Stalin’s preconditions for an invasion. Instead of keeping the units in South Korea, the United States focused on defending Japan with four army divisions, 800 aircraft, plus a small naval force stationed in Japan and the Philippines. The Communists assumed that, since the United States had not used its own forces to save the Chinese Nationalists or to protect Taiwan, it would not defend Korea. In fact, the US Joint Chiefs of Staff did regard the ROK as a strategic liability in a possible future war with the USSR. The State Department, however, believed Korea had to be defended to give credibility to US Cold War alliances and the role of the UN in collective security. Defending Korea would help correct the impression of American weakness in Asia left by the Chinese Nationalist defeat. It might discourage Communists fighting in Malaya, Indochina, and the Philippines.

The internationalized Korean War, from June 25, 1950, through July 27, 1953, went through four phases, shaped by different levels of commitment to unifying Korea by force. For Kim Il-sung and Syngman Rhee, the only victory could be the creation of one Korea, either Communist or ultra-nationalist. The North Koreans almost succeeded that first summer, but the Rhee government and half its army survived and rallied in the southeastern part of the ROK, known as the “Pusan Perimeter.” The United States committed the Eighth Army of four US Army divisions and a Marine brigade, supported by Air Force and naval aviation. The Inchon amphibious landing on September 15 and the recapture of Seoul on September 29, planned by US General Douglas MacArthur, the UN commander, delivered the final blow to the North Korean Army.

The US-UN-ROK alliance seized the opportunity to unify Korea by invading North Korea against weakened Communist resistance. From October 7 until November 26, the UN-ROK armies occupied much of North Korea under UN approval to unify the country. The ROK government tried to extend its authority by supporting an anti-Communist uprising in North Korea and hunting down and killing Communist officers, police, and party officials. The North Korean leaders fled north, knowing that China would send support.

Mao Zedong decided to use the Chinese People’s Volunteers Army (CPVA) to save North Korea, sending in a quarter of a million troops. The campaign began in late October 1950 as a desperate counterattack and continued in two offensives in November 1950 and January 1951. These unexpected offensives, marked by clever nighttime operations, drove the UN forces south of Seoul and the Han River Valley. The UN forces again rallied with reinforcements from the United States, Korea, and other UN nations. Using massed artillery and airstrikes, the Eighth Army halted the CPVA in several seesaw battles, February–March 1951. The Chinese then launched their largest offensive, designed to unify Korea as a Communist nation in April–May 1951. The UN forces defeated this offensive with concentrated firepower and sound maneuver, and a UN counteroffensive drove the Communists back across the 38th Parallel. At that point, all the belligerents accepted negotiations that ensured the survival of the ROK and DPRK. The US and USSR had global concerns, and the PRC now believed its northern flank was secure against a US-ROK-Japan anti-communist alliance. Both Koreans had to accept the leadership of their more powerful allies.

The purpose of the extended negotiations between July 1951 and July 1953 for both sides was to build up the DPRK and ROK armies and economies to a level that ensured the survival of both North and South Koriea. Major battles for marginal advantages occurred in those two years. Neither side claimed great victories, although the CPVA believed it showed it could defend against future US-ROK attacks with deep mountain fortifications and new Russian weapons. The US learned that major bombing campaigns against North Korea would not win the war but could stop Chinese offensives. After the US ensured that Syngman Rhee would accept an armistice, the fighting stopped along the current Demilitarized Zone.

The cost of the war was horrific: three million Koreans and Chinese died, two million of them Korean civilians. US-UN deaths from all causes were about 40,000 with 100,000 wounded. Despite a series of internal crises, both the ROK and DPRK have survived as Cold War anachronisms and are still enemies. The United States has a mutual security alliance with the ROK and maintains 20,000 troops there.

Allan R. Millett is the Ambrose Professor of History and director of the Eisenhower Center for American Studies at the University of New Orleans. His publications include The War for Korea, 1945–1950: A House Burning (2005) and The War for Korea, 1950–1951: They Came from the North (2010) as well as For the Common Defense: A Military History of the United States of America from the Revolutionary War through Today (2012), with Peter Maslowski.

Recommended Resources

Professor Millett recommends these resources for further information:

Cumings, Bruce. Koreaʼs Place in the Sun: A Modern History, rev. ed. New York: Norton, 2005.

Cumings, Bruce and Jon Halliday. Korea: The Unknown War. New York: Pantheon Books, 1988.

McFarland, Keith D., ed. The Korean War, 2nd ed., revised. New York and London: Routledge, 2010.

Millett, Allan R. The Korean War. (The Essential Bibliography Series). Washington, DC: Potomac Books, 2007.

Stueck, William. The Korean War: An International History. Princeton, NJ: Princeton University Press, 1995.

Tucker, Spencer, ed. The Encyclopedia of the Korean War. 2nd edition. 3 vols. Santa Barbara, CA: ABC-Clio, 2010.

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