Vietnam War: Lieutenant William Calley goes on trial for the My Lai Massacre.

The Vietnam War was an armed conflict in Vietnam, Laos, and Cambodia fought between North Vietnam and South Vietnam and their allies. North Vietnam was supported by the Soviet Union and China, while South Vietnam was supported by the United States and other anti-communist nations. The conflict was the second of the Indochina wars and a proxy war of the Cold War between the Soviet Union and US. The Vietnam War was one of the postcolonial wars of national liberation, a theater in the Cold War, and a civil war, with civil warfare a defining feature from the outset. Direct US military involvement escalated from 1965 until its withdrawal in 1973. The fighting spilled into the Laotian and Cambodian Civil Wars, which ended with all three countries becoming communist in 1975.

William Laws Calley Jr. was a United States Army officer convicted by court-martial of the murder of 22 unarmed South Vietnamese civilians in the My Lai massacre on March 16, 1968, during the Vietnam War. Calley was released to house arrest under orders by President Richard Nixon three days after his conviction. The United States District Court for the Middle District of Georgia granted him a new trial, but that ruling was overturned by the United States Court of Appeals for the Fifth Circuit. His initial life sentence having been modified to a term of 20 years and then further reduced to ten, Calley ultimately served three years of house arrest for the murders. Public opinion at the time about Calley was divided. After his dismissal from the U.S. Army and release from confinement, Calley avoided public attention.

The My Lai massacre was a United States war crime committed on 16 March 1968, involving the mass murder of unarmed civilians in Sơn Mỹ village, Quảng Ngãi province, South Vietnam, during the Vietnam War. At least 347 and up to 504 civilians, almost all women, children, and elderly men, were murdered by U.S. Army soldiers from C Company, 1st Battalion, 20th Infantry Regiment, 11th Brigade and B Company, 4th Battalion, 3rd Infantry Regiment, 11th Brigade of the 23rd (Americal) Division. Some of the women were gang-raped and their bodies mutilated, and some soldiers mutilated and raped children as young as 12. The incident was the largest massacre of civilians by U.S. forces in the 20th century.