Korean War: After four days, the No Gun Ri Massacre ends when the US Army 7th Cavalry Regiment is withdrawn.

The No Gun Ri massacre (Korean: ) occurred on July 2629, 1950, early in the Korean War, when an undetermined number of South Korean refugees were killed in a U.S. air attack and by small- and heavy-weapons fire of the American 7th Cavalry Regiment at a railroad bridge near the village of Nogeun-ri (Korean: ), 100 miles (160 km) southeast of Seoul. In 2005, a South Korean government inquest certified the names of 163 dead or missing and 55 wounded, and added that many other victims' names were not reported. The No Gun Ri Peace Foundation estimated in 2011 that 250300 were killed, mostly women and children.

The incident was little-known outside Korea until publication of an Associated Press (AP) story in 1999 in which 7th Cavalry veterans corroborated survivors' accounts. The AP also uncovered declassified U.S. Army orders to fire on approaching civilians because of reports of North Korean infiltration of refugee groups. In 2001, the U.S. Army conducted an investigation and, after previously rejecting survivors' claims, acknowledged the killings, but described the three-day event as "an unfortunate tragedy inherent to war and not a deliberate killing". The Army rejected survivors' demands for an apology and compensation, and United States President Bill Clinton issued a statement of regret, adding the next day that "things happened which were wrong".

South Korean investigators disagreed with the U.S. report, saying they believed that 7th Cavalry troops were ordered to fire on the refugees. The survivors' group called the U.S. report a "whitewash". The AP later discovered additional archival documents showing that U.S. commanders ordered troops to "shoot" and "fire on" civilians at the war front during this period; these declassified documents had been found but not disclosed by the Pentagon investigators. Among the undisclosed documents was a letter from the U.S. ambassador in South Korea stating that the U.S. military had adopted a theater-wide policy of firing on approaching refugee groups. Despite demands, the U.S. investigation was not reopened.

Prompted by the exposure of No Gun Ri, survivors of similar alleged incidents from 195051 filed reports with the Seoul government. In 2008, an investigative commission said more than 200 cases of alleged large-scale killings by the U.S. military had been registered, mostly air attacks.

The Korean War (see § Names) was a war 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. North Korea was supported by China and the Soviet Union while South Korea was supported by the United Nations, principally the United States. 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. 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. 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 to repel it. The Soviet Union was boycotting the UN for recognizing Taiwan (Republic of China) as China, and China (People's Republic of China) on the mainland 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.After the first two months of war, South Korean Army (ROKA) and American forces hastily dispatched to Korea 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. 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 US bombing campaign. Jet 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. In April 2018, the leaders of North and South Korea met at the DMZ and agreed to work toward a treaty to formally end the Korean War.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. Additionally, several million North Koreans are estimated to have fled North Korea over the course of the war.