Korean War Summary

  • Last updated on November 11, 2022

The division of Korea in 1945 after World War II at the thirty-eighth parallel into U.S. and Soviet zones of military occupation resulted in the creation of two separate governments. The determination of both the Republic of Korea (ROK) in the south and the Democratic People’s Republic of Korea (DPRK) in the north to reunify the country ignited the Korean War.

The division of Korea in 1945 after World War II at the thirty-eighth parallel into U.S. and Soviet zones of military occupation resulted in the creation of two separate governments. The determination of both the Republic of Korea (ROK) in the south and the Democratic People’s Republic of Korea (DPRK) in the north to reunify the country ignited the Korean War.

After its creation in September, 1948, North Korea had focused on supporting southern guerrillas, holding its army in reserve, and allowing South Korea to initiate most of the clashes along the thirty-eighth parallel. Starting in May, 1949, North Korea escalated its retaliation, resulting in major fighting. After Soviet arms deliveries tilted the balance in its favor, North Korea committed its regular army in August, 1949, to a campaign that drove ROK forces from salients north of the parallel. Except for a brief clash on the Ongjin Peninsula, there were few serious border incidents for the next ten months, as South Korea avoided fights it could no longer win. However, the clashes persuaded the United States to limit South Korea’s offensive military capability, denying it tanks, planes, and much heavy artillery, while bolstering North Korea’s argument to Moscow that only conquest of South Korea would remove future threats to its survival.

The North Korean Invasion

Soviet leader Joseph Stalin gave his reluctant consent to North Korea’s invasion plan in April, 1950. At dawn on June 25, 1950, the North Korean People’s Army (NKPA), led by Choe Yong Gun, launched assaults at seven points along the parallel, while staging amphibious landings on the east coast. Composed of roughly 135,000 well-trained troops, it had about 150 Soviet-built T-34 tanks, 110 combat planes, and abundant heavy artillery. The South Korean army consisted of eight combat divisions totaling 65,000 soldiers plus 33,000 support troops, with only flat-trajectory antitank guns and rocket-launching bazookas.

T<sc>ime</sc> L<sc>ine of the</sc> K<sc>orean</sc> W<sc>ar</sc>June 25, 1950Korean War begins when North Korean troops cross the thirty-eighth parallel.June 28, 1950North Koreans occupy Seoul.July 1, 1950First U.S. ground combat troops arrive in Korea.July 5, 1950Battle of Osan: North Korean forces, in their first engagement with poorly equipped and ill-trained U.S. forces, easily sweep them aside.July 16–20, 1950Taejon falls.July 29-Sept. 19, 1950Battle of the Pusan Perimeter: American and South Korean forces effectively defend the Pusan Perimeter, preventing North Korea’s military conquest of the entire peninsula.Sept. 15, 1950Inchon Landing: A decisive American and United Nations victory.Sept. 26, 1950Recapture of Seoul.Sept. 29, 1950United Nations forces drive the remainder of the North Korean forces out of South Korea.Oct. 8, 1950United Nations and Chinese forces move into North Korea.Oct. 14, 1950-Apr. 11, 1951Truman-MacArthur Confrontation: An irreconcilable dispute between General Douglas MacArthur, the head of military forces in Korea, and President Harry S. Truman tests the principle of civil control of the military.Nov. 24, 1950MacArthur launches his Home-by-Christmas Offensive to force North Korea to surrender.Nov. 26, 1950Chinese forces intervene in the war by crossing the Yalu River and attacking the exposed flanks of MacArthur’s forces.Jan., 1951Chinese forces recapture Seoul, which they maintain until March, 1951.Apr. 22–30, 1951Battle of Imjin River: Communist offensive fails to take Seoul, and the Chinese army fails to sever the primary supply line to U.S. First Corps.Aug., 1952Battle of Bloody Ridge.Sept., 1952Battle of Heartbreak Ridge.Mar. 23-July 11, 1953Battle of Pork Chop Hill: Chinese forces seize Pork Chop Hill near the end of the war.June 4, 1953China accepts voluntary repatriation.July 27, 1953Armistice ends the fighting.

The North Korean army’s main offensive thrust sent four of seven infantry divisions and 120 tanks toward Kaesong (June 25, 1950), seizing the city after just three hours. Early the next day, the North Korean forces crushed South Korea’s counterattacking Seventh Division, and fleeing South Korean soldiers abandoned countless mortars, howitzers, machine guns, and antitank guns. The North Koreans occupied Seoul on June 28, 1950. Meanwhile, in the center of the peninsula, South Korean forces mounted a spirited defense against two Northern Korean divisions and thirty tanks for five days, then withdrew to avoid being flanked from the west. Isolated on the east coast, the South Korean Eighth Division fought well and delayed the North Korean advance.

The U.S. Reaction

North Korea’s attack surprised the United States, although intelligence reports that spring had indicated that North Korea was evacuating civilians and staging a military buildup just north of the parallel. Following existing plans, President Harry S. Truman secured resolutions at the United Nations (U.N.) authorizing military assistance to South Korea. He ordered U.S. naval and air support for South Korean forces on June 25 but did not commit ground troops until five days later, approving the urgent request of General Douglas MacArthur, the occupation commander in Japan.

Reorganized remnants of the South Korean army delayed the North Korean advance south of the Han River until July 3. At the Battle of Osan (July 5, 1950), the North Korean forces, in their first engagement with understrength, poorly equipped, and ill-trained U.S. forces, easily swept aside Task Force Smith. A United Nations resolution created the U.N. Command, and Truman named MacArthur commander. After Taejon fell (July 16–20, 1950), North Korea pushed U.N. forces back to the Pusan Perimeter (July 29-September 19, 1950) in the southeastern corner of Korea. By August, the North Korean army had grown to ten divisions with the addition of South Koreans who either had been impressed into service or had voluntarily enlisted. It faced five reorganized South Korean divisions and the U.S. Twenty-fourth and Twenty-fifth Infantry Divisions and First Cavalry Division.

The Tenth Corps’ amphibious assault at the port of Inchon (September 15, 1950), thirty miles west of Seoul, met only slight resistance. The next morning, the U.S. First Marines moved eastward, with the Seventh Infantry Division protecting its right flank. Recapture of Seoul (September 26, 1950) was more difficult even after linking up with the U.S. Eighth Army that had broken out of the Pusan Perimeter, but once accomplished, United Nations forces on September 29 pushed the remnants of the North Korean forces out of South Korea.

China Enters the War

After the United States sent its Seventh Fleet into the Taiwan Strait, the People’s Republic of China feared that U.S. destruction of the North Korean army would threaten not only its own security, but its image as the leader in Asia. In July, China reorganized its Thirteenth Army Corps into the Northeastern Border Forces and deployed it along the Yalu River. On October 2, Mao Zedong persuaded his reluctant colleagues to approve sending troops to fight in Korea as “volunteers.” Beijing made a final effort to avoid entry when on October 3, Premier Zhou Enlai told India’s ambassador that if U.S. forces crossed the parallel, China would react. Most U.S. officials thought Beijing was bluffing.

General Douglas MacArthur (right) visiting the front lines, accompanied by his military secretary, Major General Courtney Whitney (second from left) and Lieutenant General Matthew B. Ridgway (center), who was later to replace him as commander of the United Nations ground forces. (National Archives)

Korean War, 1950–1953

In fact, the Truman administration had decided in August to invade North Korea, finalizing plans for forcible reunification on September 11 and giving MacArthur almost a free hand in advancing to the Yalu River. On October 8, both United Nations and Chinese forces moved into North Korea. Major engagements early in November confirmed China’s intervention, but MacArthur viewed full Chinese participation as unlikely. He launched his Home-by-Christmas Offensive on November 24 to force North Korea to capitulate. The Eighth Army and the Tenth Corps were to strike northward separately before linking to crush the North Korean forces.

The U.N. forces encountered little resistance initially, then China counterattacked in force, sending its enemy into rapid retreat. Only a harrowing withdrawal from the Chongjin Reservoir and a miraculous evacuation at Hungnam rescued the Tenth Corps from annihilation. MacArthur pressed for a naval blockade and military attacks against China, but Truman refused to widen the war, despite publicly hinting in December that he was considering using atomic weapons.

Allied Counteroffensive

General Matthew B. Ridgway, who became commander of U.N. ground forces in December, halted the retreat after Chinese forces recaptured Seoul early in January, 1951. He then implemented a strategy to inflict maximum casualties on the enemy, providing for the use of long-range artillery coupled with air attacks using napalm and rockets before ground troops with support of tanks advanced with heavy machine-gun and mortar fire. Beginning in February, Ridgway employed this “meat-grinder” strategy in Operation Killer and then in Operations Ripper and Courageous. Within three months, the U.N. forces had returned to the parallel. However, on April 22, the Chinese initiated a final effort to destroy the U.N. forces and reunite Korea. The primary target of this offensive was Seoul, with a secondary thrust at Kapyong to the east. The Chinese assault, relying as before on night attacks and superior numbers to overwhelm the enemy, was costly and ineffective against well-prepared U.N. forces, although the South Korean Sixth Division collapsed.

Despite suffering huge casualties, the Chinese redeployed eastward in May and sent thirty divisions against U.N. lines. South Korean units again broke under pressure, but reinforcements blocked a breakthrough. A U.N. counteroffensive soon threatened Chinese forces with envelopment, forcing them to retreat in disarray. China’s Fifth Phase Offensive gained nothing, and its forces sustained the worst losses of the war. By confirming the U.N. forces’ ability, through superior organization and firepower, to overcome tactics relying on massed manpower, the offensive hastened a military stalemate, thus opening the way to truce talks on July 10. By then, smaller contingents of military forces from Australia, Belgium, Canada, Colombia, Ethiopia, France, Greece, Luxembourg, the Netherlands, New Zealand, Philippines, Thailand, Turkey, South Africa, and Great Britain had joined South Korea and the United States. However, to maintain the multinational character of the U.N. forces, the United States had to comply when its allies opposed military escalation.


U.N. forces maintained battlefield pressure to achieve a quick armistice, seizing key positions north of the parallel in the Battles of Bloody Ridge (August, 1952) and Heartbreak Ridge (September, 1952). To force concessions, the United States dropped dummy atomic bombs and intensified B-29 bombing raids on North Korea, but communist MiG fighters, often with Soviet pilots, inflicted heavy damage, climaxing in the Battle of Namsi (1952). When negotiators agreed to a cease-fire line in November, the U.N. forces adopted active defense as the basis for ground strategy. The Eighth Army would undertake no major offensives and limit the scope of operations to capturing outposts in terrain suitable for temporary defense. Thereafter, a pattern emerged of patrolling and small-scale fighting with U.N. forces merely reacting to enemy contacts. Peng Dehuai, commander of Chinese forces, followed suit, causing Korea to develop into a war of attrition resembling World War I, with a static battlefield and armies depending on barbed wire, trenches, artillery, and mortars. Because both sides placed a priority on achieving an early armistice, they emphasized gaining and maintaining defense in depth, increasing troops, and stockpiling equipment behind the front line.

A U.S. gunnery squadron led by an African American sergeant holds a position north of North Korea’s Chongchon River in late November 20, 1950. The Korean War was the first U.S. conflict in which the armed services were racially integrated. (National Archives)

U.S. military leaders proposed plans for offensive action but were unable to gain approval for implementation from either the Truman or Dwight D. Eisenhower administration. However, the United States did expand the air war in the spring of 1952, attacking North Korean targets of economic importance to China and the Soviet Union. That summer, the U.N. forces bombed power installations along the Yalu and Tumen Rivers, such as the huge Suiho plant. This strategy extended to attacking targets of political significance, especially Pyongyang, using napalm as well as high explosives, with the aim of undermining enemy morale and raising to an unacceptable level the costs of stalling the truce talks.

U.S. Marines negotiating Korea’s rugged mountain terrain while closing with the enemy. (U.S. Marine Corps)

Despite the raids, the North Koreans remained inflexible, resulting in suspension of the talks in October. Both sides continued to sustain huge losses in protracted ground engagements in the spring of 1953 at Triangle, Whitehorse, and Pork Chop Hill. By then, U.S. planners had gained approval for attacks against the dams supplying water for rice cultivation in North Korea, the first attacks taking place in May.


President Eisenhower later credited the armistice ending the Korean War to success in convincing the North Koreans and Chinese that the alternative was a wider war, employing atomic weapons. Atomic coercion may have played a role in China’s accepting voluntary repatriation on June 4, 1953, thus opening the way to an armistice, but domestic economic pressures in the communist states, the Soviet bloc’s growing desire for peaceful coexistence, and the death of Joseph Stalin were more important. The communists then launched new military thrusts to gain the propaganda value of a symbolic military victory at the end of the war. China also focused attacks on South Korean forces to persuade South Korea’s government to endorse and respect the armistice agreement. Despite more than a year of U.S. effort to train and equip an enlarged South Korean army capable of postwar self-defense, only U.S. troops from the Third and Twenty-fourth Divisions, and commitment of the 187th Regimental Combat Team from Japan, halted the offensive. A U.N. counteroffensive on July 17 restored a position six miles south of the original battle line. On July 27, 1953, signing of an armistice ended fighting in the Korean War. More than 2 million Koreans died during the war, and China sustained an estimated 360,000 casualties. U.N. casualties totaled 159,000, which included 33,629 U.S. combat deaths.


Conflict between South Korea and North Korea continued into the twenty-first century, making the demilitarized zone that separates the two Koreas one of the world’s most heavily fortified and dangerous boundaries. Chinese forces withdrew, but the United States retained troops in South Korea. Periodic incidents kept alive fears of renewed war.

Categories: History