The Vietnam War ended with the fall of Saigon in 1975. On April 30, North Vietnamese forces and Viet Cong units captured Saigon, the capital of South Vietnam, after a rapid final offensive across the country.
The collapse followed the 1975 spring offensive, during which communist forces seized major cities and South Vietnamese positions. President Dương Văn Minh, who had taken office only days earlier, announced the surrender of South Vietnamese forces. Images of helicopters evacuating people from rooftops became enduring symbols of the war's final hours.
The fall of Saigon ended the existence of South Vietnam and brought the long conflict between communist North Vietnam and the US-backed South to a close. The United States had withdrawn its combat forces in 1973 under the Paris Peace Accords, but fighting between the Vietnamese sides continued afterward.
A related date often causes confusion: Vietnam was formally reunified as the Socialist Republic of Vietnam in 1976. That political reunification came after the military victory and fall of Saigon in 1975, so 1975 is the accepted answer to when the war ended. Saigon was later officially renamed Ho Chi Minh City.