The Mayaguez incident took place between Kampuchea and the United States from 12 to 15 May 1975, less than a month after the Khmer Rouge took control of the capital Phnom Penh ousting the U.S.-backed Khmer Republic. After the Khmer Rouge seized the U.S. merchant vessel SS Mayaguez in a disputed maritime area, the U.S. mounted a hastily-prepared rescue operation. U.S. Marines recaptured the ship and attacked the island of Koh Tang where it was believed that the crew were being held as hostages. Encountering stronger than expected defences on Koh Tang, three United States Air Force helicopters were destroyed during the initial assault and the Marines fought a desperate day-long battle with the Khmer Rouge before being evacuated. The Mayaguez's crew were released unharmed by the Khmer Rouge shortly after the attack on Koh Tang began. The names of the Americans killed, including three Marines left behind on Koh Tang after the battle and subsequently executed by the Khmer Rouge, are the last names on the Vietnam Veterans Memorial.

Kampuchea, officially Democratic Kampuchea (DK) from 1976 onward, was the Cambodian state from 1975 to 1979, under the totalitarian dictatorship of Pol Pot and the Communist Party of Kampuchea (CPK), commonly known as the Khmer Rouge (KR). It was established following the Khmer Rouge's capture of the capital Phnom Penh, effectively ending the United States-backed Khmer Republic of Lon Nol. After Vietnam took Phnom Penh in 1979, it was disestablished in 1982 with the creation of the CGDK in its place.