The No Gun Ri massacre occurred on July 26–29, 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, 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 250–300 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 1950–51 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.