North Korean forces crossed the 38th parallel and attacked the Republic of Korea, starting the Korean War. The rapid early advances created a crisis that soon drew in the United Nations and, later, China.
The UN Security Council condemned the attack and called for an immediate end to hostilities and withdrawal to the 38th parallel. This helped frame the conflict internationally and set the stage for UN-led military assistance to South Korea.
The UN Security Council recommended that UN members furnish assistance to repel the attack and restore peace and security in Korea. This decision enabled a broad coalition to support South Korea under UN authority.
The UN Security Council recommended that assisting forces operate under a unified command led by the United States. This established the United Nations Command (UNC), which coordinated the war effort against North Korean forces.
UNC forces carried out an amphibious landing at Inchon, outflanking North Korean forces and enabling the recapture of Seoul. The success shifted momentum and encouraged a rapid advance northward toward the prewar border and beyond.
After regaining key territory in the South, UN and South Korean forces pushed into North Korea. The northward drive brought UNC forces closer to China’s border, raising Chinese security concerns and intensifying Beijing’s debate about intervention.
Mao Zedong issued an order directing the Chinese People’s Volunteers (CPV) to enter Korea to fight the UNC alongside North Korea. China used the “volunteer” label to reduce the risk of a wider official state-to-state war, while still committing major forces.
CPV units began crossing from China into North Korea under secrecy, moving toward the front. This marked the practical start of China’s large-scale military intervention, which soon changed the balance of forces on the peninsula.
Chinese forces struck UNC and South Korean units in late October, revealing that large Chinese formations were now in the war. Early battles, including Unsan and Onjong, forced UNC commanders to reassess their advance and the risks of operating near the Chinese border.
China launched a much larger offensive that expelled UNC forces from much of North Korea. Fighting in this period included major winter battles such as Chosin Reservoir, where UN forces withdrew and evacuated under heavy pressure and extreme cold.
In a renewed offensive around the turn of the year, Chinese and North Korean troops broke through defenses near the 38th parallel. Seoul fell for a third time, showing that China’s intervention could reverse UNC gains and prolong the war.
At Chipyong-ni, US and allied forces held a surrounded defensive perimeter against Chinese attacks. The battle became an important sign that the UNC could stop major Chinese offensives and begin pushing the front back north.
China’s largest offensive of the war aimed to drive the UNC off the peninsula and regain Seoul. The offensive was halted, and UNC counterattacks followed, contributing to a shift toward more stable front lines near the 38th parallel.
With battle lines increasingly stabilized, armistice negotiations opened at Kaesong. Disputes—especially over prisoners of war and where to draw the ceasefire line—meant the talks continued while heavy fighting carried on.
The armistice was signed at Panmunjom by the United Nations Command, North Korea’s Korean People’s Army, and China’s People’s Volunteer Army. It created the Demilitarized Zone (DMZ) and ended major combat, but it did not produce a permanent peace treaty—leaving a long-term legacy of division and ongoing military tension.
Chinese Intervention in the Korean War (1950–1953)