Korean War was the first war in which a world organization, the United Nations (UN), played a military role. The Korean War was a major challenge for the United Nations, which had come into existence only five years earlier.
The Korean War began on June 25, 1950, when troops from Communist-ruled North Korea invaded South Korea. The UN called the invasion a violation of international peace and demanded that the Communists withdraw from South Korea. After the Communists kept fighting, the UN asked its member nations to give military aid to South Korea. Sixteen UN countries sent troops to help the South Koreans, and 41 countries sent military equipment or food and other supplies. The United States provided about 90 percent of the troops, military equipment, and supplies that were sent to South Korea. China fought on the side of North Korea, and the Soviet Union gave military equipment to the North Koreans.
The Korean War ended on July 27, 1953, when the UN and North Korea signed an armistice agreement. A permanent peace treaty between South Korea and North Korea has never been signed. However, United States military forces remain in South Korea to discourage a resumption of hostilities between the two parts of Korea.
The Korean War was one of the bloodiest wars in history. About a million South Korean civilians were killed and several million were made homeless. More than 560,000 UN and South Korean troops and about 1,600,000 Communist troops were killed or wounded or were reported missing.
Causes of the war
The Japanese gained control of Korea in 1895 and made it a colony of Japan in 1910. The Allies defeated Japan in World War II (1939-1945), and U.S. and Soviet forces moved into Korea. After the war, Soviet troops occupied Korea north of the 38th parallel of north latitude, an imaginary line that cuts the country about in half. American troops occupied Korea south of the 38th parallel.
In 1947, the UN General Assembly declared that elections should be held throughout Korea to choose one government for the entire country. The Soviet Union opposed this idea and would not permit elections in North Korea. On May 10, 1948, the people of South Korea elected a national assembly. The assembly set up the government of the Republic of Korea. On September 9, North Korean Communists established the Democratic People’s Republic of Korea. Both North and South Korea claimed the entire country, and their troops clashed near the border several times from 1948 to 1950. The United States removed its last troops from Korea in 1949 and indicated early in 1950 that Korea lay outside the main U.S. defense line in Asia. The Communists believed the time was right for military action.
The land war
Outbreak.
When North Korea invaded South Korea, the North Korean Army had about 135,000 soldiers. Many of the soldiers had fought for China and the Soviet Union during World War II. North Korea had airplanes, artillery, and tanks. The South Korean Army had about 95,000 soldiers, few planes or heavy guns, and no tanks. At first, the South Korean Army put up little resistance to the enemy attack.
At their greatest strength, the South Korean and UN forces consisted of almost 1,110,000 soldiers. About 590,000 were South Koreans, and about 480,000 were Americans. About 39,000 came from Australia, Belgium, Canada, Colombia, Ethiopia, France, the United Kingdom, Greece, Luxembourg, the Netherlands, New Zealand, the Philippines, South Africa, Thailand, and Turkey.
The North Korean Army grew to more than 260,000 troops during the war. China sent another 780,000 soldiers to help the North Koreans.
On the day the war began, the UN Security Council issued a resolution demanding that the Communists stop fighting and retreat to the 38th parallel. The Soviet Union, which was a member of the 11-nation Council, could have vetoed the resolution. But the Soviet Union was boycotting Council meetings to protest Nationalist China’s membership on the Council, and the Soviet delegate was absent when the vote on Korea was taken.
North Korea ignored the UN demand, and on June 27 its troops reached the outskirts of Seoul, the South Korean capital. That same day, both President Harry S. Truman and the UN took action to try to halt the Communist advance. Truman ordered U.S. air and naval forces to South Korea and the UN asked its members to aid South Korea. Truman ordered American ground forces into action on June 30. Congress supported Truman’s actions and the UN’s policy, but did not formally declare war against North Korea.
On July 1, part of the U.S. Army 24th Infantry Division flew from Japan to Busan (also spelled Pusan) at the southern tip of Korea. The next day, these troops began to move into battle positions near Daejeon (also spelled Taejon), about 75 miles (121 kilometers) south of Seoul. Troops from other UN nations began arriving in Korea shortly after the Americans.
American troops first fought the North Koreans on July 5 at Osan, 30 miles (48 kilometers) south of Seoul. The Communists had already captured Seoul.
On July 8, with the approval of the UN Security Council, Truman named General Douglas MacArthur commander in chief of the United Nations Command. The command had authority over all the Allies—South Koreans, Americans, and the troops from other UN countries. MacArthur directed Allied operations from his headquarters in Tokyo, Japan. On July 13, Lieutenant General Walton H. Walker, head of the U.S. Eighth Army, became field commander of the Allied ground forces in Korea.
Units of the U.S. Army 1st Cavalry Division and 25th Infantry Division landed in Korea on July 19 to aid the outnumbered soldiers of the 24th Division. But another city, Daejeon, fell to the Communists on July 21.
The Busan Perimeter.
The U.S. 1st Marine Provisional Brigade and the 2nd Infantry Division of the Army arrived in South Korea in late July. But the Allies were forced back to the Busan Perimeter by August 2. The Busan Perimeter was a battle line in the southeast corner of South Korea. It extended roughly from the city of Pohang on the southeast coast, west around Daegu (also spelled Taegu), and south and southeast nearly to Busan. The Nakdong (also spelled Naktong) River was the boundary of most of the area. 
The fighting at the Busan Perimeter became a turning point in the war. The North Koreans lost about 58,000 soldiers and much equipment while advancing to the area. The rapid growth of American military strength gave General Walker flexibility in the use of his troops. North Korea tried to break through the perimeter by making scattered attacks along it. Walker reacted by using reserves to meet each enemy thrust, keeping his main defense line intact. Overhead, U.S. planes provided air support and fired at the long enemy supply lines. More American tanks and artillery arrived at Busan to strengthen the defense of the perimeter.
The North Koreans saw that the Allies were gaining military superiority. They mounted a major attack and succeeded in crossing the Nakdong River on August 6. But U.S. Marines and Army forces counterattacked and prevented a general breakthrough. The North Koreans advanced to within shelling distance of Daegu, but major losses of troops and equipment forced them to pull back on August 25. The Communists attacked the Busan Perimeter again on September 3. They captured Pohang three days later, but the Allies halted the enemy advance on September 8. 
The Incheon landing
was a surprise move that changed the course of the war. In mid-September 1950, soldiers of the U.S. X (10th) Corps, accompanied by U.S. marines, sailed from Japan to Incheon (also called Inchon), on the northwest coast of South Korea. On September 15, the marines captured the port. The soldiers then came ashore. General MacArthur personally directed the amphibious landing. It required especially careful planning because the tides at Incheon vary more than 30 feet (9 meters). Each boat had to land at high tide because any boat near the shore when the tide dropped would be trapped in mud. The troops who landed at Incheon cut off the North Koreans in the Busan Perimeter area from those north of Incheon. 
Commanded by Major General Edward M. Almond, the X Corps moved toward Seoul, 24 miles (39 kilometers) northeast of Incheon. After a bitter battle, MacArthur announced the capture of Seoul on September 26. Meanwhile, General Walker’s troops fought their way out of the Busan Perimeter, inflicting heavy losses on the enemy. On September 28, they joined the X Corps near Seoul. MacArthur broadcast a demand for surrender, but North Korea rejected it.
The Allies move north.
Late in September, the Allies prepared to invade North Korea. South Korean troops crossed into North Korea on October 1 and captured the coastal cities of Wonsan, Hungnam, and Hamhung. The Eighth Army troops reached North Korea on October 8 and drove the North Koreans toward Pyongyang, the capital. They captured Pyongyang on October 19, and the Communists retreated farther north.
From Pyongyang, the Eighth Army marched through northwestern Korea toward the Yalu River, the border between North Korea and China. Parts of the X Corps drove through northeastern Korea. Some military experts later criticized this strategy of two commands.
China warned against further advances toward its border. But General MacArthur, hoping to end the war before winter set in, ordered the Allies to press on. U.S. and Chinese troops first clashed on October 25, near the Jangjin (also called Chosin or Changjin) Reservoir and at Onjong, near Pukchin. They fought until November 6, when the Chinese suddenly withdrew. The Allies then pulled back to regroup.
MacArthur and his sources of information underestimated the size of the Chinese armies. More than 300,000 Chinese troops crossed into North Korea in October and November. MacArthur believed the Allied forces outnumbered the Chinese and that the Chinese would be used for defense only. He also thought that Allied air power could prevent additional Chinese troops from entering North Korea. Political leaders in Washington and most of the Allied commanders shared MacArthur’s confidence that the war would be over by Christmas. Allied planes roamed the length of Korea, and Allied warships sailed unchallenged along the coastlines, bombarding enemy ports. MacArthur ordered another advance on November 24.
The Allies retreat.
Hopes for a quick end to the war soon disappeared. China sent a huge force against the Allies on November 26 and 27 and forced them to retreat. By the end of November, the Communists had driven a wedge between Eighth Army troops in the west and the X Corps in the east. The X Corps had remained independent from the Eighth Army. 
The Allies began to withdraw from Pyongyang on December 4. Four days later, 20,000 U.S. marines and infantrymen, surrounded by Chinese, started a historic retreat from the Jangjin Reservoir to the port of Hungnam. By Christmas Eve, 105,000 U.S. and Korean troops, 91,000 refugees, and 17,500 vehicles had been evacuated by sea from Hungnam. In the west, the Communists crossed into South Korea and captured Gorangpo, 28 miles (45 kilometers) from Seoul.
General Walker was killed in a jeep accident, and Lieutenant General Matthew B. Ridgway took command of the Eighth Army on December 27. The Communists began to attack Seoul on New Year’s Eve, and they occupied the city on Jan. 4, 1951. The Allies dug in about 25 miles (40 kilometers) south on January 10, and their retreat ended.
The “Battle for the Hills.”
Ridgway quickly restored the confidence of the Allied troops, and they soon inflicted heavy losses on the enemy. The Allies began to move north again on Jan. 16, 1951. In 15 days, they were in position to fire on Seoul. Ridgway used a new tactic calling for slower advances that would wipe out all enemy forces instead of by-passing some. 
The Allies reoccupied Seoul on March 14 without a fight. They advanced a short distance into North Korea by June. By then, the war had changed. The two sides dug in and began fighting along a battle line north of the 38th parallel. Truce talks began in July, but fighting continued for two more years. Neither side made important advances, but they fought many bitter battles for strategic positions. During this period, the war was sometimes called the “Battle for the Hills.” Battlefields included Bloody Ridge, Finger Ridge, Heartbreak Ridge, Old Baldy, and Pork Chop Hill.
One of the most controversial events of the war took place on April 11, 1951, when President Truman removed General MacArthur from command and replaced him with Ridgway. The president’s action resulted from a continuing dispute between MacArthur and defense leaders in Washington as to how the Allies should conduct the war. From the outset, MacArthur had issued public statements that there was no substitute for total victory. Now he wanted to bomb bases in Manchuria, a part of China, and use other “all-out measures.” Truman and his advisers feared such actions might lead to a third world war. Truman decided he could no longer accept MacArthur’s open disagreement with national policy. Ridgway went to Tokyo to replace MacArthur, and Lieutenant General James A. Van Fleet became commander of the Eighth Army.
Air and naval activity
The air war.
The Korean War marked the first battles between jet aircraft. Early in the conflict, Allied bombers and fighter planes based in Japan, Okinawa, and South Korea roared over North Korea unopposed. They supported Allied troops, killed enemy troops, and damaged Communist bases.
The Soviet Union soon began to supply North Korea with MiG-15 jets, and dogfights became an important part of the war. As many as 100 to 150 U.S. F-86 Sabre jets and Soviet-built MiG-15’s took part in some air battles. All the dogfights occurred over North Korea because Allied planes were not permitted to cross the Yalu River, and the MiG-15’s never flew south of the 38th parallel. Most of the battles took place in “MiG Alley,” an area between the Yalu and Pyongyang.
Late in the war, the Allies equipped bombers with shoran (_sho_rt _ra_nge _n_avigation), a new navigation technology. The equipment enabled Allied aircraft to make successful bombing raids at night.
The Allies used helicopters to carry wounded soldiers from battle zones to hospitals. Helicopter pilots made daring rescues of Allied fliers who had been shot down. For the first time, helicopters carried troops into combat.
The U.S. Air Force, Navy, and Marine Corps lost more than 2,000 planes during the war. Most of them were shot down by Communist antiaircraft guns. Allied fliers destroyed more than 1,000 Communist planes. Navy and Marine fliers killed about 100,000 Communist troops, and Air Force fliers killed about 184,800.
Naval warfare.
The Allied naval forces included 80 destroyers, 16 aircraft carriers, 8 cruisers, and 4 battleships. The U.S. Navy helped troops land by firing shells at enemy targets on shore. Wonsan, a Communist oil refining and industrial city, was under naval siege for more than two years.
Five Navy ships were sunk and 82 were hit during the war. The vessels sunk were the minesweepers Pledge, Partridge, Pirate, and Magpie, and the tug Sarsi.
The end of the war
The truce talks.
Hopes for peace increased when Jacob Malik, the Soviet delegate to the UN, proposed a cease-fire on June 23, 1951. On June 30, Ridgway, acting on instructions from Washington, suggested a meeting between Allied and Communist military officers to discuss a truce.
The truce talks began July 10 at Kaesong and were moved to Panmunjom on October 25. A settlement seemed near on November 27, when both sides agreed that the existing battle line would be the final dividing line between North and South Korea if a truce were reached within 30 days. This agreement had the effect of limiting combat, because neither side had much to gain by winning ground it might later have to surrender.
Several issues, especially voluntary repatriation of prisoners, prevented a settlement within the 30-day period. The UN Command had insisted that prisoners of both sides be allowed to choose whether or not they would return to their homelands. Many Chinese prisoners of the Allies had fought against the Communists during the Chinese civil war. They staged a violent protest against a forced return to life under Communism. Some North Korean captives also refused to return home. The Communists could not agree to the UN demand without admitting that Communism had thus far failed to secure the loyalty of all its citizens.
By late April 1952, the truce talks were firmly deadlocked over voluntary repatriation. Fighting continued along the battle line. On October 8, the UN Command adjourned the truce talks. It said the talks would resume when the Communists were ready to offer a helpful suggestion for settling the one remaining issue—voluntary repatriation.
General Mark W. Clark replaced Ridgway as commander in chief of the United Nations Command in May 1952. Dwight D. Eisenhower became president of the United States in January 1953. Then, on March 5, 1953, Soviet premier Joseph Stalin died. After Stalin’s death, Soviet leaders began talking of the need to settle disputes peacefully. On March 28, the Communists accepted an earlier offer by the UN Command for an exchange of sick and wounded prisoners. The Communists also indicated that the truce talks should be resumed. The exchange took place in April and May. The UN Command received 684 sick and wounded prisoners, including 149 Americans. It returned 6,670 Communist prisoners.
The truce talks were resumed on April 26, and the Communists accepted voluntary repatriation. They agreed to let prisoners indicate their choice to the Neutral Nations’ Repatriation Commission, which consisted of representatives of Czechoslovakia, India, Poland, Sweden, and Switzerland.
An armistice agreement was signed on July 27, 1953, and the fighting ended. A buffer zone, called the Demilitarized Zone (DMZ), divided the two sides. It was 21/2 miles (4 kilometers) wide along the final battle line. South Korea gained about 1,500 square miles (3,880 square kilometers) of territory. Both sides agreed not to increase their military strength. A Military Armistice Commission, with representatives from both sides, was set up to enforce the armistice terms. The armistice also provided for a political conference to work out a final settlement. 
After the armistice was signed, each side charged the other with torture and starvation of prisoners, and other war crimes. The North Koreans and Chinese Communists were also accused of brainwashing prisoners (see Brainwashing ). The UN General Assembly adopted a general resolution condemning such acts.
The United States spent about $67 billion on the war. Almost all parts of Korea were heavily damaged. About 1 million civilians were killed in South Korea, and property damage was estimated at more than $1 billion. Statistics were not given for civilian deaths and damage in North Korea.
Prisoner exchange.
The UN Command and the Communists completed an exchange of 88,559 prisoners in September 1953. The Neutral Nations’ Repatriation Commission took custody of prisoners who refused to return to their homelands. The armistice provided that delegates from the various countries could visit these prisoners and try to persuade them to go home. But 14,227 Chinese, 7,582 North Koreans, 325 South Koreans, 21 Americans, and 1 British prisoner refused to return. Some of these men later changed their minds.
Peace negotiations.
In 1954, Soviet officials and representatives of countries that had fought in Korea met in Geneva, Switzerland. But the negotiators failed to draw up a permanent peace plan. Nor were they able to settle the question of unifying Korea. An agreement to work toward the negotiation of a permanent peace treaty was signed by North and South Korea in 1991 and ratified in 1992. But in 1991, North Korea began to boycott the Military Armistice Commission, and China withdrew from the commission in 1994.
In April 2018, South Korean President Moon Jae-in and North Korean leader Kim Jong-un held a meeting at Panmunjom, in the DMZ. The two leaders pledged to remove nuclear weapons from the Korean Peninsula and to work toward reaching a formal peace agreement to officially end the Korean War. However, tensions soon mounted again.
