Between the escalation of US involvement in 1965 and the war's end in 1975, sustained combat, aerial bombing, defoliation campaigns, and forced-resettlement programs such as the Strategic Hamlet Program drove one of the largest internal displacements of the era, pushing millions of rural South Vietnamese into cities, refugee camps, and government-controlled hamlets. Estimates of the cumulative number of people displaced at least once vary widely, from about 5 million to more than 10 million, reflecting the difficulty of tracking repeated, overlapping displacement over a decade of conflict. The war also produced large displacement inside Laos and Cambodia as fighting spread across Indochina. Urban populations, especially Saigon's, swelled dramatically as a result.
US, South Vietnamese, North Vietnamese and Viet Cong forces conducted operations, bombing, and resettlement programs (e.g. strategic hamlets) that displaced millions of South Vietnamese civilians
Republic of Vietnam and United Nations estimates put South Vietnam at roughly 16.1 million in 1965, rising to about 19 million by 1975. The displacement counted here - strategic hamlets, free-fire zone clearances, bombing and the 1972 and 1975 offensives - fell overwhelmingly on this population rather than on the North.
Britannica, drawing on Vietnam's 1995 official release and US military records, gives up to 2,000,000 civilian dead on both sides, some 1,100,000 North Vietnamese and Viet Cong fighters, 200,000-250,000 South Vietnamese soldiers and more than 58,300 US dead — roughly 3.3 million in total. The demographic reconstruction by Hirschman, Preston and Vu (1995) yields a far lower figure of about one million Vietnamese war deaths for 1965-75, while Obermeyer, Murray and Gakidou's 2008 world-health-survey analysis produced the highest published estimate, around 3.8 million violent war deaths for 1955-2002 with a wide uncertainty interval. Hanoi's own 1995 figures are higher than most Western reconstructions; US-aligned accounts (e.g. Guenter Lewy) are lower. The range spans the demographic low and the survey-based high.
Mass killing at My Lai was established by the US Army's Peers Inquiry and the 1971 Calley court-martial; summary executions of civilians at Huế in 1968 are attributed to PAVN and NLF forces by South Vietnamese and US investigations, an attribution disputed by some scholars; the destruction of villages and forced relocation under the strategic hamlet and pacification programmes is documented in US government and congressional records of the period.
Vietnam