By Richard Baum, Ph.D., University of California, Los Angeles
The Soviet Union and the United States had occupied the northern half and southern half of Korea, respectively. This situation of partitioned occupation remained in effect until 1948, when each side set up a ‘friendly’ government in its own zone. Why did China enter the war?

Kim II-Sung, Stalin, and Mao
In North Korea, Kim II-Sung was supremely confident that he could quickly prevail in any military contest with the South. But since he was heavily dependent on Soviet military and economic assistance, he could not launch an attack on his own initiative without Soviet consent.
In the spring of 1950, Stalin, after a considerable amount of hesitation and waffling, signed off on the North Korean plan of attack.

Although China played no direct role in planning or launching the Korean War, Stalin and Mao exchanged several telegrams about the situation in Korea. Mao was initially skeptical, but once he was convinced that Stalin was going to support a North Korean invasion in any event, he reluctantly went along.
Although Stalin didn’t expect the United States to intervene, he was not willing to risk a Soviet armed conflict with the United States.
In a warning telegram to Kim II-Sung, Stalin cautioned the North Korean leader, “If you should get kicked in the teeth [by the Americans], I shall not lift a finger. You’ll have to ask Mao for all the help.”
Stalin’s warning proved prophetic.
Launching of the Korean War
North Korea’s surprise attack came on June 25, 1950. Within two days, South Korea’s outgunned, outnumbered troops were in full retreat, with many of them defecting to the North. On the third day of the war, North Korean troops entered the South Korean capital of Seoul.
Under intense pressure from the United States, the United Nations unanimously condemned the North Korean invasion as an act of unprovoked aggression.
When the UN authorized a police action to repel North Korean aggression, the United States led a multinational military force into Korea, under the command of General Douglas MacArthur. But by the time MacArthur could get substantial troops on the ground, the North Koreans had occupied approximately 90 per cent or more of the Korean peninsula.
This is a transcript from the video series The Fall and Rise of China. Watch it now, on Wondrium.
Counterattack by General MacArthur
In mid-September 1950, General MacArthur, supported by massive American supplies, transport, and combat troops, launched a surprise amphibious counterattack behind North Korean lines.
The attack on the port city of Incheon caught the North Koreans completely off guard. And the tide of battle soon turned.
By early October, the North Korean army was retreating in disarray back across the 38th parallel. In hot pursuit, MacArthur’s forces advanced into North Korea, capturing the capital city, Pyongyang, on October 19.
Chinese People’s Volunteer Army
By this time, Mao Zedong had become deeply alarmed. In early October, he gave an order to assemble a Chinese People’s Volunteer Army (or CPV) to combat the American-led U.N. forces.
At the end of October, advance units of the CPV crossed into North Korea. On November 1, they launched a surprise attack on American forces, administering a stinging defeat.

The Chinese forces then pulled back, waiting to see if the Americans had gotten the intended message—namely, that any further advance into North Korea would be met with a massive Chinese response.
When MacArthur ignored the Chinese warning, Mao ordered a full-scale military response in late November. Once again, the tide of battle turned decisively.
Hundreds of thousands of Chinese volunteers quickly overran U.N positions, inflicting heavy casualties and forcing a hasty retreat. By January of 1951, the UN forces had been driven back across the 38th parallel.
Learn more about the Chinese communism.
The Ceasefire Agreement
At that point, early in 1951, President Truman fired MacArthur for insubordination; and the Chinese side began to show some interest in negotiating a ceasefire agreement with the United Nations command.
However, Stalin refused to go along. Although neither side was winning the war, the fact that several hundred thousand American troops were bogged down in Korea meant that the United States could not utilize those troops to counter Soviet actions in Berlin or anywhere else in Europe.
Consequently, Stalin was content to let the war drag on, as it did, for another two years. The deadlock was not broken until Stalin died in March of 1953. Thereafter, a ceasefire was quickly arranged to take effect in July. The ceasefire line was the 38th parallel—an exact reversion to the status quo ante.
China and the United States
Though the Korean War ended in a draw, it nonetheless marked a decisive turning point in China’s relations with the United States.
Until China entered the war, the U.S. had been reluctant to commit itself to the defense of Chiang K’ai-shek’s exiled Nationalist regime on Taiwan. In the aftermath of the Korean War, however, the U.S. government sharply revised its strategic calculus with respect to Taiwan.
Chiang K’ai-shek was now a vital Free World ally in a struggle against world communism. Accordingly, in December 1954, President Dwight Eisenhower signed a Treaty of Mutual Defense with Chiang’s government-in-exile in Taiwan.
U.S.-Taiwan Mutual Defense Treaty
Pursuant to these aims of the U.S.-Taiwan Mutual Defense Treaty, ships from the U.S. Seventh Fleet patrolled the 90-mile-wide waters of the Taiwan Strait to protect Taiwan and prevent the PRC from launching an amphibious attack.
For the next 20 years, these naval patrols remained a potent symbol of the U.S. commitment to defend Taiwan.
Korean War and China’s National Security
While the Korean War served to bolster Taiwan’s relations with the United States, it had a far more negative impact on China’s national security. Chinese troops suffered more than one million casualties in the war.
China lost the opportunity to conclude its civil war by liberating Taiwan. The PRC was condemned as an aggressor by the United Nations for intervening in Korea, although it was a defensive intervention in the first instance.
As a result of the war, the Unites States entered into a series of military treaties designed to contain Chinese Communism. These included the U.S.-Taiwan Defense Treaty, the Southeast Asia Treaty Organization (or SEATO), and the ANZUS Pact, which involved the U.S., Australia, and New Zealand.
Learn more about Chiang K’ai-shek’s army.
Benefits of the Korean War on China
On at least two counts, the People’s Republic scored clear gains. The Chinese Communists were able to upgrade their armed forces. During the war, they received substantial Soviet military assistance, including up-to-date Soviet tanks, artillery, and some 3,000 warplanes.
By fighting the world’s most powerful country to a virtual standstill in Korea, Mao Zedong greatly elevated his and China’s stature both within the socialist camp and in the Third World.
Common Questions about China and the Korean War
North Korea launched a surprise attack on South Korea on June 25, 1950.
Mao gave an order to assemble a Chinese People’s Volunteer Army (or CPV) to combat the American-led U.N. forces in North Korea.
The US-Taiwan Defense Treaty, the Southeast Asia Treaty Organization (or SEATO), and the ANZUS Pact with the U.S., Australia, and New Zealand were some of the treaties the US entered into to contain Chinese Communism.