The War You Never Learned About: A History of the Korean War - Documentary Film (1952)

The CIA WW2 Guide to Sabotaging a Workplace: https://www.patreon.com/posts/cia-guide-to-77295599Show more

The Korean War (also known by other names) was fought between North Korea and South Korea from 1950 to 1953. The war began on 25 June 1950 when North Korea invaded South Korea following clashes along the border and rebellions in South Korea.[32][33][34] North Korea was supported by China and the Soviet Union while South Korea was supported by the United States and allied countries. The fighting ended with an armistice on 27 July 1953.

In 1910, Imperial Japan annexed Korea, where it ruled for 35 years until its surrender at the end of World War II on 15 August 1945.[c] The United States and the Soviet Union divided Korea along the 38th parallel into two zones of occupation. The Soviets administered the northern zone and the Americans administered the southern zone. In 1948, as a result of Cold War tensions, the occupation zones became two sovereign states. A socialist state, the Democratic People's Republic of Korea, was established in the north under the totalitarian communist leadership of Kim Il-sung, while a capitalist state, the Republic of Korea, was established in the south under the authoritarian, autocratic leadership of Syngman Rhee. Both governments of the two new Korean states claimed to be the sole legitimate government of all of Korea, and neither accepted the border as permanent.

North Korean military (Korean People's Army, KPA) forces crossed the border and drove into South Korea on 25 June 1950.[35] Joseph Stalin had final decision power and several times demanded North Korea postpone the invasion, until he gave final approval in spring 1950.[36] The United Nations Security Council denounced the North Korean move as an invasion and authorized the formation of the United Nations Command and the dispatch of forces to Korea[37] to repel it.[38][39] The Soviet Union was boycotting the UN for recognizing Taiwan (Republic of China) as China,[40] and the People's Republic of China was not recognized by the UN, so neither could support their ally North Korea at the Security Council meeting. Twenty-one countries of the United Nations eventually contributed to the UN force, with the United States providing around 90% of the military personnel.[41]

After the first two months of war, South Korean Army (ROKA) and hastily dispatched American forces were on the point of defeat, retreating to a small area behind a defensive line known as the Pusan Perimeter. In September 1950, a risky amphibious UN counteroffensive was launched at Incheon, cutting off KPA troops and supply lines in South Korea. Those who escaped envelopment and capture were forced back north. UN forces invaded North Korea in October 1950 and moved rapidly towards the Yalu River—the border with China—but on 19 October 1950, Chinese forces of the People's Volunteer Army (PVA) crossed the Yalu and entered the war.[35] The UN retreated from North Korea after the First Phase Offensive and the Second Phase Offensive. Chinese forces were in South Korea by late December.

In these and subsequent battles, Seoul was captured four times, and communist forces were pushed back to positions around the 38th parallel, close to where the war had started. After this, the front stabilized, and the last two years were a war of attrition. The war in the air, however, was never a stalemate. North Korea was subject to a massive U.S. bombing campaign. Jet-powered fighters confronted each other in air-to-air combat for the first time in history, and Soviet pilots covertly flew in defense of their communist allies.

The fighting ended on 27 July 1953 when the Korean Armistice Agreement was signed. The agreement created the Korean Demilitarized Zone (DMZ) to separate North and South Korea, and allowed the return of prisoners. However, no peace treaty was ever signed, and the two Koreas are technically still at war, engaged in a frozen conflict.[42][43] In April 2018, the leaders of North and South Korea met at the DMZ[44] and agreed to work toward a treaty to end the Korean War formally.[45]

The Korean War was among the most destructive conflicts of the modern era, with approximately 3 million war fatalities and a larger proportional civilian death toll than World War II or the Vietnam War. It incurred the destruction of virtually all of Korea's major cities, thousands of massacres by both sides, including the mass killing of tens of thousands of suspected communists by the South Korean government, and the torture and starvation of prisoners of war by the North Koreans. North Korea became among the most heavily bombed countries in history.[46] 1.5 million North Koreans are estimated to have fled North Korea over the course of the war.[47]
Names
Korean War
South Korean name
Hangul 6·25 전쟁 or 한국 전쟁
Hanja 六二五戰爭 or 韓國戰爭
Transcriptions
North Korean name
Chosŏn'gŭl 조국해방전쟁
Hancha 祖國解放戰爭
Transcriptions

In South Korea, the war is usually referred to as the "625 War" (6·25 전쟁; 六二五戰爭), the "625 Upheaval" (6·25 동란; 六二五動亂; yugio dongnan), or simply "625", reflecting the date of its commencement on 25 June.[48]

In North Korea, the war is officially referred to as the "Fatherland Liberation War" (Choguk haebang chŏnjaeng) or alternatively the "Chosŏn [Korean] War" (조선전쟁; Chosŏn chŏnjaeng).[49]

In mainland China, the segment of the war after the intervention of the People's Volunteer Army is most commonly and officially known as the "Resisting America and Assisting Korea War"[50] (Chinese: 抗美援朝战争; pinyin: Kàngměi Yuáncháo Zhànzhēng), although the term "Chosŏn War" (Chinese: 朝鮮戰爭; pinyin: Cháoxiǎn Zhànzhēng) is sometimes used unofficially. The term "Hán (Korean) War" (Chinese: 韓戰; pinyin: Hán Zhàn) is most commonly used in Taiwan (Republic of China), Hong Kong and Macau.

In the U.S., the war was initially described by President Harry S. Truman as a "police action", as the United States never formally declared war on its opponents and the operation was conducted under the auspices of the United Nations.[51] It has been sometimes referred to in the English-speaking world as "The Forgotten War" or "The Unknown War" because of the lack of public attention it received both during and after the war, relative to the global scale of World War II, which preceded it, and the subsequent angst of the Vietnam War, which succeeded it.[52][53]
Background
Imperial Japanese rule (1910–1945)
Main article: Korea under Japanese rule

Imperial Japan severely diminished the influence of China over Korea in the First Sino-Japanese War (1894–95), ushering in the short-lived Korean Empire.[54] A decade later, after defeating Imperial Russia in the Russo-Japanese War (1904–05), Japan made the Korean Empire its protectorate with the Eulsa Treaty in 1905, then annexed it with the Japan–Korea Annexation Treaty in 1910. After that, the Korean Empire fell and Korea was directly ruled by Japan from 1910 to 1945.[55]

Many Korean nationalists fled the country. The Provisional Government of the Republic of Korea was founded in 1919 in Nationalist China. It failed to achieve international recognition, failed to unite the various nationalist groups, and had a fractious relationship with its U.S.-based founding president, Syngman Rhee.[56] From 1919 to 1925 and beyond, Korean communists led internal and external warfare against the Japanese.[57][58]

In China, the nationalist National Revolutionary Army and the communist People's Liberation Army (PLA) helped organize Korean refugees against the Japanese military, which had also occupied parts of China. The Nationalist-backed Koreans, led by Yi Pom-Sok, fought in the Burma Campaign (December 1941 – August 1945). The communists, led among others by Kim Il-sung, fought the Japanese in Korea and Manchuria.[59]

At the Cairo Conference in November 1943, China, the United Kingdom and the United States all decided that "in due course Korea shall become free and independent".[60]
Korea divided (1945–1949)
Main article: Division of Korea

At the Tehran Conference in November 1943 and the Yalta Conference in February 1945, the Soviet Union promised to join its allies in the Pacific War within three months of the victory in Europe. Germany officially surrendered on 8 May 1945, and the USSR declared war on Japan and invaded Manchuria on 8 August 1945, three months later. This was three days after the atomic bombing of Hiroshima.[58][61] By 10 August, the Red Army had begun to occupy the north of Korea.[62]

On the night of 10 August in Washington, U.S. Colonels Dean Rusk and Charles H. Bonesteel III were assigned to divide Korea into Soviet and U.S. occupation zones and proposed the 38th Parallel as the dividing line. This was incorporated into the U.S. General Order No. 1, which responded to the Japanese surrender on 15 August. Explaining the choice of the 38th Parallel, Rusk observed, "even though it was further north than could be realistically reached by U. S. [sic] forces in the event of Soviet disagreement ... we felt it important to include the capital of Korea in the area of responsibility of American troops". He noted that he was "faced with the scarcity of U.S. forces immediately available and time and space factors which would make it difficult to reach very far north before Soviet troops could enter the area".[63][64] As Rusk's comments indicate, the U.S. doubted whether the Soviet government would agree to this.[65][66][67][68] Soviet leader Joseph Stalin, however, maintained his wartime policy of co-operation, and on 16 August, the Red Army halted at the 38th Parallel for three weeks to await the arrival of U.S. forces in the south.[62]

On 7 September 1945, General Douglas MacArthur issued Proclamation No. 1 to the people of Korea, announcing U.S. military control over Korea south of the 38th parallel and establishing English as the official language during military control.[69]

On 8 September 1945, U.S. Lieutenant General John R. Hodge arrived in Incheon to accept the Japanese surrender south of the 38th Parallel.[66] Appointed as military governor, Hodge directly controlled South Korea as head of the United States Army Military Government in Korea (USAMGIK 1945–48).[70]

In December 1945, Korea was administered by a U.S.–Soviet Union Joint Commission, as agreed at the Moscow Conference, with the aim of granting independence after a five-year trusteeship.[71][72] The idea was not popular among Koreans and riots broke out.[55] To contain them, the USAMGIK banned strikes on 8 December 1945 and outlawed the PRK Revolutionary Government and the PRK People's Committees on 12 December 1945.[73] Following further large-scale civilian unrest,[74] the USAMGIK declared martial law.

Citing the inability of the Joint Commission to make progress, the U.S. government decided to hold an election under United Nations auspices with the aim of creating an independent Korea. The Soviet authorities and the Korean Communists refused to co-operate on the grounds that it would not be fair, and many South Korean politicians boycotted it.[75][76] A general election was held in the South on 10 May 1948.[77][78] North Korea held parliamentary elections three months later on 25 August.[79]

The resultant South Korean government promulgated a national political constitution on 17 July 1948, and elected Syngman Rhee as President on 20 July 1948. This election is generally considered to have been manipulated by the Rhee regime. The Republic of Korea (South Korea) was established on 15 August 1948. In the Soviet Korean Zone of Occupation, the Soviet Union agreed to the establishment of a communist government[77] led by Kim Il-sung.[80]

The Soviet Union withdrew its forces from Korea in 1948, and U.S. troops withdrew in 1949.[81][82]
Chinese Civil War (1945–1949)
Main articles: Chinese Civil War and Chinese Communist Revolution

With the end of the war with Japan, the Chinese Civil War resumed in earnest between the Communists and Nationalists. While the Communists were struggling for supremacy in Manchuria, they were supported by the North Korean government with matériel and manpower.[83] According to Chinese sources, the North Koreans donated 2,000 railway cars worth of supplies while thousands of Koreans served in the Chinese PLA during the war.[84] North Korea also provided the Chinese Communists in Manchuria with a safe refuge for non-combatants and communications with the rest of China.[83]

The North Korean contributions to the Chinese Communist victory were not forgotten after the creation of the People's Republic of China (PRC) in 1949. As a token of gratitude, between 50,000 and 70,000 Korean veterans that served in the PLA were sent back along with their weapons, and they later played a significant role in the initial invasion of South Korea.[83] China promised to support the North Koreans in the event of a war against South Korea.[85]

After the formation of the PRC, the PRC government named the Western nations, led by the U.S., as the biggest threat to its national security.[86] Basing this judgment on multiple factors, including the idea of a Chinese century of humiliation at the hands of Western powers beginning in the mid-19th century,[87] U.S. support for the Nationalists during the Chinese Civil War,[88] and the ideological struggles between revolutionaries and reactionaries,[89] the PRC Chinese leadership believed that China would become a critical battleground in the U.S.' crusade against Communism.[90] As a countermeasure and to elevate China's standing among the worldwide Communist movements, the PRC leadership adopted a foreign policy that actively promoted Communist revolutions throughout territories on China's periphery.[91]
Communist insurgency in South Korea (1948–1950)

By 1948, a large-scale, North Korea-backed insurgency had broken out in the southern half of the peninsula. This was exacerbated by the ongoing undeclared border war between the Koreas, which saw division-level engagements and thousands of deaths on both sides.[92] The ROK in this time was almost entirely trained and focused on counterinsurgency, rather than conventional warfare. They were equipped and advised by a force of a few hundred American officers, who were largely successful in helping the ROKA to subdue guerrillas and hold its own against North Korean military (Korean People's Army, KPA) forces along the 38th parallel.[93] Approximately 8,000 South Korean soldiers and police died in the insurgent war and border clashes.[94]

The first socialist uprising occurred without direct North Korean participation, though the guerrillas still professed support for the northern government. Beginning in April 1948 on the isolated island of Jeju, the campaign saw mass arrests and repression by the South Korean government in the fight against the South Korean Labor Party, resulting in a total of 30,000 violent deaths, among them 14,373 civilians (of whom ~2,000 were killed by rebels and ~12,000 by ROK security forces). The Yeosu–Suncheon rebellion overlapped with it, as several thousand army defectors waving red flags massacred right-leaning families. This resulted in another brutal suppression by the government and between 2,976 and 3,392 deaths. By May 1949, both uprisings had been crushed.

Insurgency reignited in the spring of 1949 when attacks by guerrillas in the mountainous regions (buttressed by army defectors and North Korean agents) increased. Insurgent activity peaked in late 1949 as the ROKA engaged so-called People's Guerrilla Units. Organized and armed by the North Korean government, and backed up by 2,400 KPA commandos who had infiltrated through the border, these guerrillas launched a large offensive in September aimed at undermining the South Korean government and preparing the country for the KPA's arrival in force. This offensive failed.[95] However, by this point, the guerrillas were firmly entrenched in the Taebaek-san region of the North Gyeongsang Province (around Taegu), as well as in the border areas of the Gangwon Province.[96]

While the insurgency was ongoing, the ROKA and KPA engaged in multiple battalion-sized battles along the border, starting in May 1949.[93] Serious border clashes between South and North continued on 4 August 1949, when thousands of North Korean troops attacked South Korean troops occupying territory north of the 38th Parallel. The 2nd and 18th ROK Infantry Regiments repulsed initial attacks in Kuksa-bong (above the 38th Parallel)[97] and Ch'ungmu,[citation needed] and at the end of the clashes ROK troops were "completely routed".[98] Border incidents decreased significantly by the start of 1950.[96]

Meanwhile, counterinsurgency efforts in the South Korean interior intensified; persistent operations, paired with worsening weather conditions, eventually denied the guerrillas sanctuary and wore away their fighting strength. North Korea responded by sending more troops to link up with existing insurgents and build more partisan cadres; the number of North Korean infiltrators had reached 3,000 soldiers in 12 units by the start of 1950, but all of these units were destroyed or scattered by the ROKA.[99] On 1 October 1949, the ROKA launched a three-pronged assault on the insurgents in South Cholla and Taegu. By March 1950, the ROKA claimed 5,621 guerrillas killed or captured and 1,066 small arms seized. This operation crippled the insurgency. Soon after, the North Koreans made two final attempts to keep the uprising active, sending two battalion-sized units of infiltrators under the commands of Kim Sang-ho and Kim Moo-hyon. The first battalion was reduced in annihilation to a single man over the course of several engagements by the ROKA 8th Division. The second battalion was annihilated by a two-battalion hammer-and-anvil maneuver by units of the ROKA 6th Division, resulting in a loss toll of 584 KPA guerrillas (480 killed, 104 captured) and 69 ROKA troops killed, plus 184 wounded.[100] By spring of 1950, guerrilla activity had mostly subsided; the border, too, was calm.[101]
Prelude to war (1950)

By 1949, South Korean and U.S. military actions had reduced the active number of indigenous communist guerrillas in the South from 5,000 to 1,000. However, Kim Il-sung believed that widespread uprisings had weakened the South Korean military and that a North Korean invasion would be welcomed by much of the South Korean population. Kim began seeking Stalin's support for an invasion in March 1949, traveling to Moscow to attempt to persuade him.[102]

Stalin initially did not think the time was right for a war in Korea. PLA forces were still embroiled in the Chinese Civil War, while U.S. forces remained stationed in South Korea.[103] By spring 1950, he believed that the strategic situation had changed: PLA forces under Mao Zedong had secured final victory in China, U.S. forces had withdrawn from Korea, and the Soviets had detonated their first nuclear bomb, breaking the U.S. atomic monopoly. As the U.S. had not directly intervened to stop the communist victory in China, Stalin calculated that they would be even less willing to fight in Korea, which had much less strategic significance. The Soviets had also cracked the codes used by the U.S. to communicate with their embassy in Moscow, and reading these dispatches convinced Stalin that Korea did not have the importance to the U.S. that would warrant a nuclear confrontation.[104] Stalin began a more aggressive strategy in Asia based on these developments, including promising economic and military aid to China through the Sino-Soviet Treaty of Friendship, Alliance, and Mutual Assistance.[105]

In April 1950, Stalin gave Kim permission to attack the government in the South under the condition that Mao would agree to send reinforcements if needed. For Kim, this was the fulfillment of his goal to unite Korea after its division by foreign powers. Stalin made it clear that Soviet forces would not openly engage in combat, to avoid a direct war with the U.S.[106] Kim met with Mao in May 1950. Historical analyses regarding Mao's approval of Kim's plans differ.[107]: 28–9  Nikita Khrushchev's memoirs were long viewed as the most authoritative source, and Khrushchev wrote that Mao approved Kim's plans because Mao viewed the matter as one for the Korean people to decide for themselves.[107]: 29  Citing recent scholarship, Zhao Suisheng, writing in 2022, contends that Mao did not approve of Kim's plans in advance, opposing them over concerns that the U.S. would intervene and that China could be dragged into the conflict.[107]: 29  By some accounts, Mao agreed to support the North Korean invasion despite these concerns, as China desperately needed the economic and military aid promised by the Soviets.[108] However, Mao sent more ethnic Korean PLA veterans to Korea and promised to move an army closer to the Korean border.[109] Once Mao's commitment was secured, preparations for war accelerated.[110][111]

Soviet generals with extensive combat experience from the Second World War were sent to North Korea as the Soviet Advisory Group. These generals completed the plans for the attack by May.[112] The original plans called for a skirmish to be initiated in the Ongjin Peninsula on the west coast of Korea. The North Koreans would then launch a counterattack that would capture Seoul and encircle and destroy the ROK. The final stage would involve destroying South Korean government remnants and capturing the rest of South Korea, including the ports.[113]

On 7 June 1950, Kim Il-sung called for a Korea-wide election on 5–8 August 1950 and a consultative conference in Haeju on 15–17 June 1950. On 11 June, the North sent three diplomats to the South as a peace overture which Rhee rejected outright.[106] On 21 June, Kim Il-Sung revised his war plan to involve a general attack across the 38th Parallel, rather than a limited operation in the Ongjin Peninsula. Kim was concerned that South Korean agents had learned about the plans and that South Korean forces were strengthening their defenses. Stalin agreed to this change of plan.[114]

While these preparations were underway in the North, there were frequent clashes along the 38th Parallel, especially at Kaesong and Ongjin, many initiated by the South.[33][34] The ROK was being trained by the U.S. Korean Military Advisory Group (KMAG). On the eve of war, KMAG commander General William Lynn Roberts voiced utmost confidence in the ROK and boasted that any North Korean invasion would merely provide "target practice".[115] For his part, Syngman Rhee repeatedly expressed his desire to conquer the North, including when U.S. diplomat John Foster Dulles visited Korea on 18 June.[116]

Although some South Korean and U.S. intelligence officers predicted an attack from the North, similar predictions had been made before and nothing had happened.[117] The Central Intelligence Agency noted the southward movement by the KPA, but assessed this as a "defensive measure" and concluded an invasion was "unlikely".[118] On 23 June, UN observers inspected the border and did not detect that war was imminent.[119]
Comparison of forces

Throughout 1949 and 1950, the Soviets continued arming North Korea. After the Communist victory in the Chinese Civil War, ethnic Korean units in the PLA were sent to North Korea.[120] Chinese involvement was extensive from the beginning, building on previous collaboration between the Chinese and Korean communists during the Chinese Civil War. In the fall of 1949, two PLA divisions composed mainly of Korean-Chinese troops (the 164th and 166th) entered North Korea, followed by smaller units throughout the rest of 1949; these troops brought with them not only their experience and training, but also their weapons and other equipment, changing little but their uniforms. The reinforcement of the KPA with PLA veterans continued into 1950, with the 156th Division and several other units of the former Fourth Field Army arriving (also with their equipment) in February; the PLA 156th Division was reorganized as the KPA 7th Division. By mid-1950, between 50,000 and 70,000 former PLA troops had entered North Korea, forming a significant part of the KPA's strength on the eve of the war's beginning.[121] Several generals, such as Lee Kwon-mu, were PLA veterans born to ethnic Koreans in China. The combat veterans and equipment from China, the tanks, artillery and aircraft supplied by the Soviets, and rigorous training increased North Korea's military superiority over the South, armed by the U.S. military with mostly small arms, but no heavy weaponry such as tanks.[122] While older histories of the conflict often referred to these ethnic Korean PLA veterans as being sent from northern Korea to fight in the Chinese Civil War before being sent back, recent Chinese archival sources studied by Kim Donggill indicate that this was not the case. Rather, the soldiers were indigenous to China (part of China's longstanding ethnic Korean community) and were recruited to the PLA in the same way as any other Chinese citizen.[123]

According to the first official census in 1949, the population of North Korea numbered 9,620,000,[124] and by mid-1950, North Korean forces numbered between 150,000 and 200,000 troops, organized into 10 infantry divisions, one tank division, and one air force division, with 210 fighter planes and 280 tanks, who captured scheduled objectives and territory, among them Kaesong, Chuncheon, Uijeongbu and Ongjin. Their forces included 274 T-34-85 tanks, 200 artillery pieces, 110 attack bombers, and some 150 Yak fighter planes, and 35 reconnaissance aircraft. In addition to the invasion force, the North had 114 fighters, 78 bombers, 105 T-34-85 tanks, and some 30,000 soldiers stationed in reserve in North Korea.[66] Although each navy consisted of only several small warships, the North and South Korean navies fought in the war as seaborne artillery for their armies.

In contrast, the South Korean population was estimated at 20 million[125] and its army was unprepared and ill-equipped. As of 25 June 1950, the ROK had 98,000 soldiers (65,000 combat, 33,000 support), no tanks (they had been requested from the U.S. military, but requests were denied), and a 22-plane air force comprising 12 liaison-type and 10 AT-6 advanced-trainer airplanes. Large U.S. garrisons and air forces were in Japan,[126] but only 200–300 U.S. troops were in Korea.[127]
Course of the war
Territory often changed hands early in the war, until the front stabilized.
Chinese and communist forces (Soviet Union)
North Korean forces
South Korean, U.S. and United Nations forces
Hundreds of thousands of South Koreans fled south in mid-1950 after the North Korean army invaded.

At dawn on Sunday, 25 June 1950, the KPA crossed the 38th Parallel behind artillery fire.[128] The KPA justified its assault with the claim that ROK troops attacked first and that the KPA were aiming to arrest and execute the "bandit traitor Syngman Rhee".[129] Fighting began on the strategic Ongjin Peninsula in the west.[130][131] There were initial South Korean claims that the 17th Regiment captured the city of Haeju, and this sequence of events has led some scholars to argue that the South Koreans fired first.[130][132]

Whoever fired the first shots in Ongjin, KPA forces attacked all along the 38th Parallel within an hour. The KPA had a combined arms force including tanks supported by heavy artillery. The ROK had no tanks, anti-tank weapons or heavy artillery to stop such an attack. In addition, the South Koreans committed their forces in a piecemeal fashion and these were routed in a few days.[133]

On 27 June, Rhee evacuated from Seoul with some of the government. On 28 June, at 2 am, the ROK blew up the Hangang Bridge across the Han River in an attempt to stop the KPA. The bridge was detonated while 4,000 refugees were crossing it and hundreds were killed.[134][135] Destroying the bridge also trapped many ROK units north of the Han River.[133] In spite of such desperate measures, Seoul fell that same day. A number of South Korean National Assemblymen remained in Seoul when it fell, and forty-eight subsequently pledged allegiance to the North.[136]

On 28 June, Rhee ordered the massacre of suspected political opponents in his own country.[137]

In five days, the ROK, which had 95,000 troops on 25 June, was down to less than 22,000 troops. In early July, when U.S. forces arrived, what was left of the ROK were placed under U.S. operational command of the United Nations Command.[138]
Factors in U.S. intervention

The Truman administration was unprepared for the invasion. Korea was not included in the strategic Asian Defense Perimeter outlined by United States Secretary of State Dean Acheson.[139] Truman himself was at his home in Independence, Missouri.[140] Military strategists were more concerned with the security of Europe against the Soviet Union than East Asia.[141] At the same time, the administration was worried that a war in Korea could quickly escalate without American intervention. Said diplomat John Foster Dulles in a cable: "To sit by while Korea is overrun by unprovoked armed attack would start a disastrous chain of events leading most probably to world war."[142]

While there was initial hesitance by some in the U.S. government to get involved in the war, considerations about Japan played a part in the ultimate decision to engage on behalf of South Korea. Especially after the fall of China to the Communists, U.S. experts on East Asia saw Japan as the critical counterweight to the Soviet Union and China in the region. While there was no U.S. policy dealing with South Korea directly as a national interest, its proximity to Japan increased the importance of South Korea. Said Kim: "The recognition that the security of Japan required a non-hostile Korea led directly to President Truman's decision to intervene ... The essential point ... is that the American response to the North Korean attack stemmed from considerations of U.S. policy toward Japan."[143][144]

Another major consideration was the possible Soviet reaction if the U.S. intervened. The Truman administration was fearful that a war in Korea was a diversionary assault that would escalate to a general war in Europe once the United States committed in Korea. At the same time, "[t]here was no suggestion from anyone that the United Nations or the United States could back away from [the conflict]".[145] Yugoslavia—a possible Soviet target because of the Tito-Stalin Split—was vital to the defense of Italy and Greece, and the country was first on the list of the National Security Council's post-North Korea invasion list of "chief danger spots".[146] Truman believed if aggression went unchecked, a chain reaction would be initiated that would marginalize the UN and encourage Communist aggression elsewhere. The UN Security Council approved the use of force to help the South Koreans, and the U.S. immediately began using air and naval forces that were in the area to that end. The Truman administration still refrained from committing troops on the ground because some advisers believed the North Koreans could be stopped by air and naval power alone.[147]

The Truman administration was still uncertain if the attack was a ploy by the Soviet Union or just a test of U.S. resolve. The decision to commit ground troops became viable when a communiqué was received on 27 June indicating the Soviet Union would not move against U.S. forces in Korea.[148] The Truman administration now believed it could intervene in Korea without undermining its commitments elsewhere.
United Nations Security Council Resolutions
Further information: List of United Nations Security Council resolutions concerning North Korea

On 25 June 1950, the United Nations Security Council unanimously condemned the North Korean invasion of South Korea, with UN Security Council Resolution 82. The Soviet Union, a veto-wielding power, had boycotted the Council meetings since January 1950, protesting Taiwan's occupation of China's permanent seat in the UN Security Council.[149] After debating the matter, the Security Council, on 27 June 1950, published Resolution 83 recommending member states provide military assistance to the Republic of Korea. On 27 June, President Truman ordered U.S. air and sea forces to help South Korea. On 4 July, the Soviet Deputy Foreign Minister accused the U.S. of starting armed intervention on behalf of South Korea.[150]

The Soviet Union challenged the legitimacy of the war for several reasons. The ROK intelligence upon which Resolution 83 was based came from U.S. Intelligence; North Korea was not invited as a sitting temporary member of the UN, which violated UN Charter Article 32; and the fighting was beyond the UN Charter's scope, because the initial north–south border fighting was classed as a civil war. Because the Soviet Union was boycotting the Security Council at the time, legal scholars posited that deciding upon an action of this type required the unanimous vote of all the five permanent members including the Soviet Union.[151][152]

Within days of the invasion, masses of ROK soldiers—of dubious loyalty to the Syngman Rhee regime—were retreating southwards or defecting en masse to the northern side, the KPA.[57]
United States' response (July–August 1950)
A group of soldiers readying a large gun in some brush
A U.S. howitzer position near the Kum River, 15 July
Man of the Year, the American soldier on Time magazine cover, 1951

As soon as word of the attack was received,[153] Acheson informed President Truman that the North Koreans had invaded South Korea.[154][155] Truman and Acheson discussed a U.S. invasion response and agreed that the U.S. was obligated to act, comparing the North Korean invasion with Adolf Hitler's aggressions in the 1930s, with the conclusion being that the mistake of appeasement must not be repeated.[156] Several U.S. industries were mobilized to supply materials, labor, capital, production facilities, and other services necessary to support the military objectives of the Korean War.[157] President Truman later explained that he believed fighting the invasion was essential to the U.S. goal of the global containment of communism as outlined in the National Security Council Report 68 (NSC 68) (declassified in 1975):

Communism was acting in Korea, just as Hitler, Mussolini and the Japanese had ten, fifteen, and twenty years earlier. I felt certain that if South Korea was allowed to fall, Communist leaders would be emboldened to override nations closer to our own shores. If the Communists were permitted to force their way into the Republic of Korea without opposition from the free world, no small nation would have the courage to resist threat and aggression by stronger Communist neighbors.[158]

In August 1950, the President and the Secretary of State obtained the consent of Congress to appropriate $12 billion for military action in Korea.[155]

Because of the extensive defense cuts and the emphasis placed on building a nuclear bomber force, none of the services were in a position to make a robust response with conventional military strength. General Omar Bradley, Chairman of the Joint Chiefs of Staff, was faced with reorganizing and deploying a U.S. military force that was a shadow of its World War II counterpart.[159][160]

Acting on Secretary of State Acheson's recommendation, President Truman ordered Supreme Commander for the Allied Powers in Japan General Douglas MacArthur to transfer matériel to the South Korean military while giving air cover to the evacuation of U.S. nationals. The President disagreed with advisers who recommended unilateral U.S. bombing of the North Korean forces and ordered the U.S. Seventh Fleet to protect the Republic of China (Taiwan), whose government asked to fight in Korea. The United States denied Taiwan's request for combat, lest it provoke a PRC retaliation.[161] Because the United States had sent the Seventh Fleet to "neutralize" the Taiwan Strait, Chinese premier Zhou Enlai criticized both the UN and U.S. initiatives as "armed aggression on Chinese territory".[162]
The drive south and Pusan (July–September 1950)
G.I. comforting a grieving infantryman
M24 Chaffee light tanks of the U.S. Army's 25th Infantry Division wait for an assault of North Korean T-34-85 tanks at Masan
Crew of an M-24 tank along the Nakdong River front, August 1950
Pershing and Sherman tanks of the 73rd Heavy Tank Battalion at the Pusan Docks, Korea.

The Battle of Osan, the first significant U.S. engagement of the Korean War, involved the 540-soldier Task Force Smith, which was a small forward element of the 24th Infantry Division which had been flown in from Japan.[163] On 5 July 1950, Task Force Smith attacked the KPA at Osan but without weapons capable of destroying the KPA tanks. The KPA defeated the U.S. soldiers; the result was 180 American dead, wounded, or taken prisoner. The KPA progressed southwards, pushing back U.S. forces at Pyongtaek, Chonan, and Chochiwon, forcing the 24th Division's retreat to Taejeon, which the KPA captured in the Battle of Taejon; the 24th Division suffered 3,602 dead and wounded and 2,962 captured, including its commander, Major General William F. Dean.[164]

By August, the KPA steadily pushed back the ROK and the Eighth United States Army southwards.[165] The impact of the Truman administration's defense budget cutbacks was now keenly felt, as U.S. troops fought a series of costly rearguard actions. Facing a veteran and well-led KPA force, and lacking sufficient anti-tank weapons, artillery or armor, the Americans retreated and the KPA advanced down the Korean Peninsula.[166][167] During their advance, the KPA purged South Korea's intelligentsia by killing civil servants and intellectuals. On 20 August, General MacArthur warned North Korean leader Kim Il-sung that he would be held responsible for the KPA's atrocities.[168] By September, UN forces were hemmed into a small corner of southeast Korea, near Pusan. This 230-kilometre (140-mile) perimeter enclosed about 10% of Korea, in a line partially defined by the Nakdong River.

Although Kim's early successes led him to predict he would end the war by the end of August, Chinese leaders were more pessimistic. To counter a possible U.S. deployment, Zhou Enlai secured a Soviet commitment to have the Soviet Union support Chinese forces with air cover, and deployed 260,000 soldiers along the Korean border, under the command of Gao Gang. Zhou commanded Chai Chengwen to conduct a topographical survey of Korea, and directed Lei Yingfu, Zhou's military advisor in Korea, to analyze the military situation in Korea. Lei concluded that MacArthur would most likely attempt a landing at Incheon.[169][170] After conferring with Mao that this would be MacArthur's most likely strategy, Zhou briefed Soviet and North Korean advisers of Lei's findings, and issued orders to PLA commanders deployed on the Korean border to prepare for U.S. naval activity in the Korea Strait.[171]

In the resulting Battle of Pusan Perimeter (August–September 1950), the UN forces withstood KPA attacks meant to capture the city at the Naktong Bulge, P'ohang-dong, and Taegu. The United States Air Force (USAF) interrupted KPA logistics with 40 daily ground support sorties, which destroyed 32 bridges, halting most daytime road and rail traffic. KPA forces were forced to hide in tunnels by day and move only at night.[172] To deny military equipment and supplies to the KPA, the USAF destroyed logistics depots, petroleum refineries, and harbors, while the U.S. Navy air forces attacked transport hubs. Consequently, the overextended KPA could not be supplied throughout the south.[173] On 27 August, 67th Fighter Squadron aircraft mistakenly attacked facilities in Chinese territory and the Soviet Union called the UN Security Council's attention to China's complaint about the incident.[174] The U.S. proposed that a commission of India and Sweden determine what the U.S. should pay in compensation, but the Soviets vetoed the U.S. proposal.[175][176]

Meanwhile, U.S. garrisons in Japan continually dispatched soldiers and military supplies to reinforce defenders in the Pusan Perimeter.[177] Tank battalions deployed to Korea directly from the U.S. mainland from the port of San Francisco to the port of Pusan, the largest Korean port. By late August, the Pusan Perimeter had some 500 medium tanks battle-ready.[178] In early September 1950, UN forces outnumbered the KPA 180,000 to 100,000 soldiers.[54][179]
Battle of Incheon (September 1950)
Main article: Battle of Incheon
General Douglas MacArthur, UN Command CiC (seated), observes the naval shelling of Incheon from USS Mount McKinley, 15 September 1950
Combat in the streets of Seoul
Pershing tanks in downtown Seoul during the Second Battle of Seoul in September 1950. In the foreground, United Nations troops round up North Korean prisoners-of-war.

Against the rested and rearmed Pusan Perimeter defenders and their reinforcements, the KPA were undermanned and poorly supplied; unlike the UN forces, they lacked naval and air support.[180] To relieve the Pusan Perimeter, General MacArthur recommended an amphibious landing at Incheon, near Seoul and well over 160 km (100 mi) behind the KPA lines.[181] On 6 July, he ordered Major General Hobart R. Gay, commander of the U.S. 1st Cavalry Division, to plan the division's amphibious landing at Incheon; on 12–14 July, the 1st Cavalry Division embarked from Yokohama, Japan, to reinforce the 24th Infantry Division inside the Pusan Perimeter.[182]

Soon after the war began, General MacArthur began planning a landing at Incheon, but the Pentagon opposed him.[181] When authorized, he activated a combined U.S. Army and Marine Corps, and ROK force. The U.S. X Corps, led by Major General Edward Almond, consisted of 40,000 soldiers of the 1st Marine Division, the 7th Infantry Division and around 8,600 ROK soldiers.[183] By 15 September, the amphibious assault force faced few KPA defenders at Incheon: military intelligence, psychological warfare, guerrilla reconnaissance, and protracted bombardment facilitated a relatively light battle. However, the bombardment destroyed most of the city of Incheon.[184]
Breakout from the Pusan Perimeter
Main articles: Pusan Perimeter offensive, UN September 1950 counteroffensive, and Second Battle of Seoul

On 16 September Eighth Army began its breakout from the Pusan Perimeter. Task Force Lynch,[185][186] 3rd Battalion, 7th Cavalry Regiment, and two 70th Tank Battalion units (Charlie Company and the Intelligence–Reconnaissance Platoon) advanced through 171.2 km (106.4 mi) of KPA territory to join the 7th Infantry Division at Osan on 27 September.[182] X Corps rapidly defeated the KPA defenders around Seoul, thus threatening to trap the main KPA force in Southern Korea.[187] On 18 September, Stalin dispatched General H. M. Zakharov to North Korea to advise Kim Il-sung to halt his offensive around the Pusan perimeter and to redeploy his forces to defend Seoul. Chinese commanders were not briefed on North Korean troop numbers or operational plans. As the overall commander of Chinese forces, Zhou Enlai suggested that the North Koreans should attempt to eliminate the UN forces at Incheon only if they had reserves of at least 100,000 men; otherwise, he advised the North Koreans to withdraw their forces north.[188]

On 25 September, Seoul was recaptured by UN forces. U.S. air raids caused heavy damage to the KPA, destroying most of its tanks and much of its artillery. KPA troops in the south, instead of effectively withdrawing north, rapidly disintegrated, leaving Pyongyang vulnerable.[188] During the general retreat, only 25,000 to 30,000 KPA soldiers managed to reach the KPA lines.[189][190] On 27 September, Stalin convened an emergency session of the Politburo, in which he condemned the incompetence of the KPA command and held Soviet military advisers responsible for the defeat.[188]
UN forces invade North Korea (September–October 1950)
Main article: UN offensive into North Korea

On 27 September, MacArthur received the top secret National Security Council Memorandum 81/1 from Truman reminding him that operations north of the 38th Parallel were authorized only if "at the time of such operation there was no entry into North Korea by major Soviet or Chinese Communist forces, no announcements of intended entry, nor a threat to counter our operations militarily".[191] On 29 September, MacArthur restored the government of the Republic of Korea under Syngman Rhee.[188] On 30 September, U.S. Defense Secretary George Marshall sent an eyes-only message to MacArthur: "We want you to feel unhampered tactically and strategically to proceed north of the 38th parallel."[191] During October, the South Korean police executed people who were suspected to be sympathetic to North Korea,[192] and similar massacres were carried out until early 1951.[193] The Joint Chiefs of Staff on 27 September sent to General MacArthur a comprehensive directive to govern his future actions: the directive stated that the primary goal was the destruction of the KPA, with unification of the Korean Peninsula under Rhee as a secondary objective "if possible"; the Joint Chiefs added that this objective was dependent on whether or not the Chinese and Soviets would intervene, and was subject to changing conditions.[194]
U.S. Air Force attacking railroads south of Wonsan on the eastern coast of North Korea

On 30 September, Zhou Enlai warned the U.S. that China was prepared to intervene in Korea if the U.S. crossed the 38th Parallel. Zhou attempted to advise KPA commanders on how to conduct a general withdrawal by using the same tactics that allowed Chinese communist forces to successfully escape Chiang Kai-shek's encirclement campaigns in the 1930s, but by some accounts, KPA commanders did not use these tactics effectively.[195] Historian Bruce Cumings argues, however, that the KPA's rapid withdrawal was strategic, with troops melting into the mountains from where they could launch guerrilla raids on the UN forces spread out on the coasts.[196]

By 1 October 1950, the UN Command repelled the KPA northwards past the 38th Parallel; the ROK advanced after them, into North Korea.[197] MacArthur made a statement demanding the KPA's unconditional surrender.[198] Six days later, on 7 October, with UN authorization, the UN Command forces followed the ROK forces northwards.[199] The X Corps landed at Wonsan (in southeastern North Korea) and Riwon (in northeastern North Korea) on 26 October, but these cities had already been captured by ROK forces.[200] The Eighth U.S. Army drove up western Korea and captured Pyongyang on 19 October 1950.[201] The 187th Airborne Regimental Combat Team made their first of two combat jumps during the Korean War on 20 October 1950 at Sunchon and Sukchon. The mission was to cut the road north going to China, preventing North Korean leaders from escaping from Pyongyang; and to rescue U.S. prisoners of war. At month's end, UN forces held 135,000 KPA prisoners of war. As they neared the Sino-Korean border, the UN forces in the west were divided from those in the east by 80–161 km (50–100 mi) of mountainous terrain.[202] In addition to the 135,000 captured, the KPA had also suffered some 200,000 soldiers killed or wounded for a total of 335,000 casualties since the end of June 1950, and had lost 313 tanks (mostly T-34/85 models). A mere 25,000 KPA regulars retreated across the 38th Parallel, as their military had entirely collapsed. The UN forces on the peninsula numbered 229,722 combat troops (including 125,126 Americans and 82,786 South Koreans), 119,559 rear area troops, and 36,667 U.S. Air Force personnel.[203]

Taking advantage of the UN Command's strategic momentum against the communists, MacArthur believed it necessary to extend the Korean War into China to destroy depots supplying the North Korean war effort. Truman disagreed, and ordered caution at the Sino-Korean border.[204]
China intervenes (October–December 1950)
Chinese forces cross the frozen Yalu River.

On 30 June 1950, five days after the outbreak of the war, Zhou Enlai, premier of the PRC and vice-chairman of the Central Military Committee of the CCP (CMCC), decided to send a group of Chinese military intelligence personnel to North Korea to establish better communications with Kim II-Sung as well as to collect firsthand materials on the fighting. One week later, on 7 July, Zhou and Mao chaired a conference discussing military preparations for the Korean Conflict. Another conference took place on 10 July. Here, it was decided that the Thirteenth Army Corps under the Fourth Field Army of the People's Liberation Army (PLA), one of the best-trained and -equipped units in China, would be immediately transformed into the Northeastern Border Defense Army (NEBDA) to prepare for "an intervention in the Korean War if necessary". On 13 July, the CMCC formally issued the order to establish the NEBDA, appointing Deng Hua, the commander of the Fifteenth Army Corps and one of the most talented commanders of the Chinese Civil War, to coordinate all preparation efforts.[205]: 11–12 

On 20 August 1950, Premier Zhou Enlai informed the UN that "Korea is China's neighbor... The Chinese people cannot but be concerned about a solution of the Korean question". Thus, through neutral-country diplomats, China warned that in safeguarding Chinese national security, they would intervene against the UN Command in Korea.[204] President Truman interpreted the communication as "a bald attempt to blackmail the UN", and dismissed it.[206] Mao ordered that his troops should be ready for action by the end of August. Stalin, by contrast, was reluctant to escalate the war with a Chinese intervention.[207]

On 1 October 1950, the day that UN troops crossed the 38th Parallel, the Soviet ambassador forwarded a telegram from Stalin to Mao and Zhou requesting that China send five to six divisions into Korea, and Kim Il-sung sent frantic appeals to Mao for Chinese military intervention. At the same time, Stalin made it clear that Soviet forces themselves would not directly intervene.[198]
Three commanders of PVA during the Korean War. From left to right: Chen Geng (1952); Peng Dehuai (1950–1952); and Deng Hua (1952–1953).

In a series of emergency meetings that lasted from 2 to 5 October, Chinese leaders debated whether to send Chinese troops into Korea. There was considerable resistance among many leaders, including senior military leaders, to confronting the U.S. in Korea.[208] Mao strongly supported intervention, and Zhou was one of the few Chinese leaders who firmly supported him. After Lin Biao politely refused Mao's offer to command Chinese forces in Korea (citing his upcoming medical treatment),[209] Mao decided that Peng Dehuai would be the commander of the Chinese forces in Korea after Peng agreed to support Mao's position.[209] Mao then asked Peng to speak in favor of intervention to the rest of the Chinese leaders. After Peng made the case that if U.S. troops conquered Korea and reached the Yalu, they might cross it and invade China, the Politburo agreed to intervene in Korea.[210] On 4 August 1950, with a planned invasion of Taiwan aborted due to the heavy U.S. naval presence, Mao reported to the Politburo that he would intervene in Korea when the PLA's Taiwan invasion force was reorganized into the PLA North East Frontier Force.[211] On 8 October 1950, Mao redesignated the PLA North East Frontier Force as the People's Volunteer Army (PVA).[212]

To enlist Stalin's support, Zhou and a Chinese delegation arrived in Moscow on 10 October, at which point they flew to Stalin's home on the Black Sea.[213] There, they conferred with the top Soviet leadership, which included Joseph Stalin as well as Vyacheslav Molotov, Lavrentiy Beria and Georgy Malenkov. Stalin initially agreed to send military equipment and ammunition but warned Zhou that the Soviet Air Force would need two or three months to prepare any operations. In a subsequent meeting, Stalin told Zhou that he would only provide China with equipment on a credit basis and that the Soviet Air Force would only operate over Chinese airspace, and only after an undisclosed period of time. Stalin did not agree to send either military equipment or air support until March 1951.[214] Mao did not find Soviet air support especially useful, as the fighting was going to take place on the south side of the Yalu.[215] Soviet shipments of matériel, when they did arrive, were limited to small quantities of trucks, grenades, machine guns, and the like.[216]

In a meeting on 13 October, the Politburo of the Chinese Communist Party decided that China would intervene even in the absence of Soviet air support, basing its decision on a belief that superior morale could defeat an enemy that had superior equipment.[217] Immediately on his return to Beijing on 18 October 1950, Zhou met with Mao Zedong, Peng Dehuai and Gao Gang, and the group ordered two hundred thousand PVA troops to enter North Korea, which they did on 19 October.[218] UN aerial reconnaissance had difficulty sighting PVA units in daytime, because their march and bivouac discipline minimized aerial detection.[219] The PVA marched "dark-to-dark" (19:00–03:00), and aerial camouflage (concealing soldiers, pack animals, and equipment) was deployed by 05:30. Meanwhile, daylight advance parties scouted for the next bivouac site. During daylight activity or marching, soldiers were to remain motionless if an aircraft appeared, until it flew away;[219] PVA officers were under order to shoot security violators. Such battlefield discipline allowed a three-division army to march the 460 km (286 mi) from An-tung, Manchuria, to the combat zone in some 19 days. Another division night-marched a circuitous mountain route, averaging 29 km (18 mi) daily for 18 days.[66]

Meanwhile, on 15 October 1950, President Truman and General MacArthur met at Wake Island. This meeting was much publicized because of the General's discourteous refusal to meet the President on the continental United States.[220] To President Truman, MacArthur speculated there was little risk of Chinese intervention in Korea,[221] and that the PRC's opportunity for aiding the KPA had lapsed. He believed the PRC had some 300,000 soldiers in Manchuria and some 100,000–125,000 soldiers at the Yalu River. He further concluded that, although half of those forces might cross south, "if the Chinese tried to get down to Pyongyang, there would be the greatest slaughter" without air force protection.[189][222]
Soldiers from the US 2nd Infantry Division in action near the Ch'ongch'on River (20 November 1950).
A column of the US 1st Marine Division move through Chinese lines during their breakout from the Chosin Reservoir.
Map of the UN retreat in the wake of Chinese intervention.

After secretly crossing the Yalu River on 19 October, the PVA 13th Army Group launched the First Phase Offensive on 25 October, attacking the advancing UN forces near the Sino-Korean border. This military decision made solely by China changed the attitude of the Soviet Union. Twelve days after PVA troops entered the war, Stalin allowed the Soviet Air Force to provide air cover and supported more aid to China.[223] After inflicting heavy losses on the ROK II Corps at the Battle of Onjong, the first confrontation between Chinese and U.S. military occurred on 1 November 1950. Deep in North Korea, thousands of soldiers from the PVA 39th Army encircled and attacked the U.S. 8th Cavalry Regiment with three-prong assaults—from the north, northwest, and west—and overran the defensive position flanks in the Battle of Unsan.[224] The surprise assault resulted in the UN forces retreating back to the Ch'ongch'on River, while the PVA unexpectedly disappeared into mountain hideouts following victory. It is unclear why the Chinese did not press the attack and follow up their victory.[citation needed]

The UN Command, however, were unconvinced that the Chinese had openly intervened because of the sudden PVA withdrawal. On 24 November, the Home-by-Christmas Offensive was launched with the U.S. Eighth Army advancing in northwest Korea, while U.S. X Corps attacked along the Korean east coast. But the PVA were waiting in ambush with their Second Phase Offensive, which they executed at two sectors: in the East at the Chosin Reservoir and in the Western sector at Ch'ongch'on River.[citation needed]

On 13 November, Mao appointed Zhou Enlai the overall commander and coordinator of the war effort, with Peng as field commander.[218] On 25 November, on the Korean western front, the PVA 13th Army Group attacked and overran the ROK II Corps at the Battle of the Ch'ongch'on River, and then inflicted heavy losses on the U.S. 2nd Infantry Division on the UN forces' right flank.[225] Believing that they could not hold against the PVA, the Eighth Army began to retreat from North Korea crossing the 38th Parallel in mid-December.[226] UN morale hit rock bottom when Lieutenant General Walton Walker, commander of the U.S. Eighth Army, was killed on 23 December 1950 in an automobile accident.[citation needed]

In the east, on 27 November, the PVA 9th Army Group initiated the Battle of Chosin Reservoir. Here, the UN forces fared comparatively better: like the Eighth Army, the surprise attack also forced X Corps to retreat from northeast Korea, but they were, in the process, able to break out from the attempted encirclement by the PVA and execute a successful tactical withdrawal. X Corps managed to establish a defensive perimeter at the port city of Hungnam on 11 December and were able to evacuate by 24 December to reinforce the badly depleted U.S. Eighth Army to the south.[227][228] During the evacuation, about 193 shiploads of UN forces and matériel (approximately 105,000 soldiers, 98,000 civilians, 17,500 vehicles, and 350,000 tons of supplies) were evacuated to Pusan.[229] The SS Meredith Victory was noted for evacuating 14,000 refugees, the largest rescue operation by a single ship, even though it was designed to hold 12 passengers. Before escaping, the UN forces razed most of Hungnam city, with particular attention to the port facilities.[189][230] The UN retreat from North Korea also saw the massive evacuation from the capital city of Pyongyang. In early December, UN forces, including the British Army's 29th Infantry Brigade, evacuated Pyongyang, along with large numbers of refugees.[231] Around 4.5 million North Koreans are estimated to have fled from North Korea to either the South or elsewhere abroad.[232] On 16 December 1950, President Truman declared a national state of emergency with Presidential Proclamation No. 2914, 3 C.F.R. 99 (1953),[233] which remained in force until 14 September 1978.[d] The next day, 17 December 1950, Kim Il-sung was deprived of the right of command of KPA by China.[234]

China justified its entry into the war as a response to what it described as "American aggression in the guise of the UN".[211] Chinese decision-makers feared that the American-led invasion of North Korea was part of a U.S. strategy to invade China ultimately. They were also worried about rising counterrevolutionary activity at home.[217] MacArthur's public statements that he wanted to extend the Korean War into China, and return the Kuomintang to power reinforced this fear.[217] Later, the Chinese claimed that U.S. bombers had violated PRC national airspace on three separate occasions and attacked Chinese targets before China intervened.[235][236]
Fighting around the 38th Parallel (January–June 1951)

A ceasefire presented by the UN to the PRC shortly after the Battle of the Ch'ongch'on River on 11 December 1950, was rejected by the Chinese government, which was convinced of the PVA's invincibility after its victory in that battle and the wider Second Phase Offensive, and also wanted to demonstrate China's desire for a total victory through the expulsion of the UN forces from Korea.[237][238] With Lieutenant General Matthew Ridgway assuming the command of the U.S. Eighth Army on 26 December, the PVA and the KPA launched their Third Phase Offensive (also known as the "Chinese New Year's Offensive") on New Year's Eve of 1950/51. Utilizing night attacks in which UN fighting positions were encircled and then assaulted by numerically superior troops who had the element of surprise, the attacks were accompanied by loud trumpets and gongs, which fulfilled the double purpose of facilitating tactical communication and mentally disorienting the enemy. UN forces initially had no familiarity with this tactic, and as a result, some soldiers panicked, abandoning their weapons and retreating to the south.[239] The offensive overwhelmed UN forces, allowing the PVA and KPA to capture Seoul for the second time on 4 January 1951. Following this, the CPV party committee issued orders regarding tasks during rest and reorganization on 8 January 1951, outlining Chinese war goals. The orders read: "the central issue is for the whole party and army to overcome difficulties ... to improve tactics and skills. When the next campaign starts ... we will annihilate all enemies and liberate all Korea." In his telegram to Peng on 14 January, Mao stressed the importance of preparing for "the last battle" in the spring in order to "fundamentally resolve the [Korean] issue".[240]
B-26 Invaders bomb logistics depots in Wonsan, North Korea, 1951

These setbacks prompted General MacArthur to consider using nuclear weapons against the Chinese or North Korean interiors, intending radioactive fallout zones to interrupt the Chinese supply chains.[241] However, upon the arrival of the charismatic General Ridgway, the esprit de corps of the bloodied Eighth Army immediately began to revive.[242]

UN forces retreated to Suwon in the west, Wonju in the center, and the territory north of Samcheok in the east, where the battlefront stabilized and held.[239] The PVA had outrun its logistics capability and thus were unable to press on beyond Seoul as food, ammunition, and matériel were carried nightly, on foot and bicycle, from the border at the Yalu River to the three battle lines.[243] In late January, upon finding that the PVA had abandoned their battle lines, General Ridgway ordered a reconnaissance-in-force, which became Operation Thunderbolt (25 January 1951).[244] A full-scale advance followed, which fully exploited the UN's air superiority,[245] concluding with the UN forces reaching the Han River and recapturing Wonju.[244]

Following the failure of ceasefire negotiations in January, the United Nations General Assembly passed Resolution 498 on 1 February, condemning the PRC as an aggressor, and called upon its forces to withdraw from Korea.[246][247]

In early February, the ROK 11th Division ran an operation to destroy guerrillas and pro-DPRK sympathizers in Southern Korea.[248] During the operation, the division and police conducted the Geochang massacre and Sancheong–Hamyang massacre.[248] In mid-February, the PVA counterattacked with the Fourth Phase Offensive and achieved initial victory at Hoengseong. However, the offensive was soon blunted by U.S. IX Corps at Chipyong-ni in the center.[244] The U.S. 23rd Regimental Combat Team and the French Battalion fought a short but desperate battle that broke the attack's momentum.[244] The battle is sometimes known as the "Gettysburg of the Korean War": 5,600 South Korean, U.S., and French troops were surrounded on all sides by 25,000 PVA. UN forces had previously retreated in the face of large PVA/KPA forces instead of getting cut off, but this time, they stood and fought, and won.[249]
U.S. Marines move out over rugged mountain terrain while closing with North Korean forces.

In the last two weeks of February 1951, Operation Thunderbolt was followed by Operation Killer, carried out by the revitalized Eighth Army. It was a full-scale, battlefront-length attack staged for maximum exploitation of firepower to kill as many KPA and PVA troops as possible.[244] Operation Killer concluded with U.S. I Corps re-occupying the territory south of the Han River, and IX Corps capturing Hoengseong.[250] On 7 March 1951, the Eighth Army attacked with Operation Ripper, expelling the PVA and the KP