The People's Republic of China played an important role in the Korean War. Prior to North Korea's invasion of South Korea in June 1950, China sent many Chinese ethnic Koreans who had served with the Chinese People's Liberation Army (PLA) to serve in North Korea's Korean People's Army (KPA), with them making up 47% of the North's invasion force. China directly entered the conflict in October 1950, with the People's Volunteer Army (PVA) units crossing the Yalu River in secret, in support of North Korea. Subsequently, Chinese forces launched multiple major campaigns against United Nations Command and South Korean troops, playing a crucial role in prolonging and shaping the war's outcome. Throughout the conflict, the PVA engaged in extensive combat operations, logistics build-up, and defensive strategies, eventually deploying over one million personnel at the height of its involvement. The Chinese intervention influenced both battlefield dynamics and the broader geopolitical landscape, contributing to the eventual stalemate and the signing of the Korean Armistice Agreement in 1953. The PVA's participation resulted in significant casualties and economic costs for China, and also solidified its status as a regional power in the early Cold War period.

Background

North Korea had good relations with China from the period of the recently concluded Chinese Civil War. In the late 1940s, after World War II ended and the Chinese Civil War resumed, while the Chinese Communist Party was struggling for supremacy in Manchuria, they were supported by the North Korean government with matériel and manpower. 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. North Korea also provided the Chinese Communists in Manchuria with a safe refuge for non-combatants and communications with the rest of China. As a token of gratitude, between 50,000 and 70,000 Chinese ethnic Korean veterans who 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. These former Chinese soldiers turned North Korean soldiers made up 47% of North Korea's 148,680-man army by June 1950. While some older histories of the war referred to these ethnic Korean PLA veterans as being originally from northern Korea who went to fight in the Chinese Civil War before being sent back, recent Chinese archives indicate that these soldiers were actually part of China's longstanding ethnic Korean community. This includes several high ranking North Korean generals who played an important role in the invasion including Lee Kwon-mu. China also promised to support the North Koreans in the event of a war against South Korea.

North Korean leader Kim Il Sung met with Chairman of the Chinese Communist Party Mao Zedong in May 1950 and differing historical interpretations of the meeting have been put forward. According to Barbara Barnouin and Yu Changgeng, Mao agreed to support Kim despite concerns of American intervention, as China desperately needed the economic and military aid promised by the Soviets. Kathryn Weathersby cites Soviet documents which said Kim secured Mao's support. Along with Mark O'Neill, she says this accelerated Kim's war preparations.Mark O'Neill, "Soviet Involvement in the Korean War: A New View from the Soviet-Era Archives", OAH Magazine of History, Spring 2000, p. 21. Chen Jian said Mao never seriously challenged Kim's plans and Kim had every reason to inform Stalin that he had obtained Mao's support. Citing more recent scholarship, Zhao Suisheng said Mao did not approve of Kim's war proposal and requested verification from Stalin, who did so via a telegram. Mao accepted the decision made by Kim and Stalin to unify Korea but cautioned Kim over possible US intervention.

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. Several generals, such as Lee Kwon-mu, were PLA veterans born to ethnic Koreans in China. 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, as part of China's longstanding ethnic Korean community, and were recruited to the PLA in the same way as any other Chinese citizen.Zhihua Shen. "A Misunderstood Friendship: Mao Zedong, Kim Il-sung, and Sino–North Korean Relations, 1949–1976". Columbia University Press, September 2018.

Although the Chinese leadership did not make the decision to enter the Korean War until United Nations (UN) forces crossed the 38th Parallel in October 1950,.. it had been preparing for the possibility ever since United States intervened in Korea in June 1950... (The Korean War begun on 25 June 1950) Two weeks later, on 7 July, Chinese Premier Zhou Enlai and Mao chaired a conference discussing military preparations for Chinese involvement the conflict. Another conference took place on 10 July. Here, it was decided that the 13th Army Corps under the 4th Field Army of the People's Liberation Army (PLA), one of the best-trained and best-equipped units in China, would be immediately transformed into the Northeastern Border Defense Army (NEBDA; also translated as the North East Frontier Force, NEFF) to prepare for "an intervention in the Korean War if necessary". On 13 July, Mao issued the order to establish the NEBDA in Manchuria, appointing Deng Hua, the commander of the 15th Army Corps and one of the most talented commanders of the Chinese Civil War, to coordinate all preparation efforts.. Aside from the 38th, 39th and 40th Infantry Corps originally belonged to the 13th Army, the NEFF also included the 42nd Infantry Corps, three artillery divisions, one anti-aircraft regiments and three transport regiments—in total more than 250,000 men..

Mao convened the full Politburo of the Chinese Communist Party to debate his decision to enter the war.

China enters the war After the People's Republic of China entered the Korean War in October 1950 by designating the People's Liberation Army (PLA) North East Frontier Force as the People's Volunteer Army (PVA), the PVA spent the next two years and nine months in combat operations and five years and three months in garrison duties. Its last elements did not leave Korea until as late as 1958..

Although the United Nations Command (UNC) forces were under United States command, this army was officially a UN "police" force. In order to avoid an open war with the U.S. and other United Nations (UN) members, the People's Republic of China explicitly deployed the People's Liberation Army (PLA) under the name "volunteer army". No declaration of war ever existed between China and the UN (or the USA's) forces.

First Phase Campaign (October 25 – November 5, 1950) On October 19, 1950, and under strict secrecy, the NEFF officially crossed the Yalu River under the name Chinese People's Volunteer Army (PVA),. although advance scouting parties had been spotted by UN forces as early as October 13.. On October 23, the PLA 50th and 66th Corps were attached to the PVA 13th Army in order to reinforce the defenses at Sinuiju and Chongju area.. At the same time, the 13th Army Headquarters was disbanded to increase coordination between PVA Headquarters and its field units..

Second Phase Campaign (November 25 – December 24, 1950)

On August 26, 1950, the Chinese Central Military Commission concluded that PVA will eventually be composed of the PLA 9th, 13th and 19th Army—totaling 700,000 men—by the spring of 1951... On October 11, 1950, Mao authorized the PLA 9th Army to be moved from Shandong province to Manchuria as reserves to the 13th Army in Korea.. On November 10, 1950, the PLA 9th Army entered Korea in order to reinforce Chinese forces on the east side of Taebaek Mountains... This development brought the total PVA strength to 450,000,. including 380,000 combat personnel.

Third Phase Campaign (December 31, 1950 – January 8, 1951) Although the PVA succeeded in expelling UN forces from North Korea during the Second Phase Campaign, about a quarter of its original 450,000 men became casualties in the aftermath of the campaign.. On December 17, Mao ordered the PVA 9th Army to be removed from the front for rest and refit,. reducing the PVA combat personnel to 230,000 by the end of December 1950.. UN intelligence, on the other hand, estimated that only 171,117 combat personal were actually available for the PVA on January 1, 1951.. By the end of 1950, however, the North Korean People's Army returned to the front and brought about 75,000 men to make up for the Chinese losses..

Fourth Phase Campaign (January 30 – April 21, 1951)

By the end of the Third Phase Campaign, the PVA had become completely exhausted after fighting nonstop since the start of the Chinese intervention,. and its combat personnel was further reduced to 217,000.. According to PVA Deputy Commander Han Xianchu's evaluation of PVA, "many regiments and battalions are completely combat ineffective, with some divisions only half strength".. On February 7, 1951, Mao decided that PLA 3rd, 19th, 20th Army and 47th Corps—from Sichuan, Gansu, Hebei and Hunan provinces respectively—would enter Korea to replace the PVA 13th Army currently on the front... But despite the massive mobilization effort, only the 26th Corps from the recovering PVA 9th Army actually arrived at the front during March 1951...

Fifth Phase Campaign (April 22 – June 10, 1951)

In the aftermath of the Fourth Phase Campaign, the PVA 13th Army's 38th and 42nd Corps were forced to leave the frontline for rest and refit, while its 50th and 66th Corps were evacuated back to China.. Following Mao's orders, however, the PLA 3rd and 19th Army began to enter Korea in February 1951,. alongside four field artillery divisions, two long range artillery divisions, four anti-aircraft divisions, one multiple rocket launcher division and four tank regiments.. The PVA 9th Army had also returned to the front in April 1951 after four months of rest. Those development soon brought the total PVA strength to over one million men, including 548,000 combat personnel and 180,000 logistics personnel... On April 21, 1951, the 39th and 40th Corps of the PVA 13th Army were placed under 9th Army's control.. On April 22, 1951, the reorganized PVA launched a full-scale offensive in Korea, and the resulting clashes between Chinese and UN forces is often described as the largest battle of the entire Korean War..

UN limited offensives (June 11 – December 3, 1951) The Fifth Phase Campaign ended as a complete operational disaster for the PVA... About 12 divisions from the PVA 3rd and 19th Army were rendered combat ineffective, and between 85,000 and 110,000 men became casualties in the aftermath... With the frontline on the verge of collapse in the face of UN attacks,. the 42nd and 47th Corps were sent as reinforcements on May 27, 1951. But the UN forces soon broke off their pursuit on June 1, and armistice negotiations started on July 10, 1951..