Peter Davis's 1974 Vietnam War indictment. Won Best Documentary Oscar; remains a benchmark for political documentary.
From Wikipedia
Hearts and Minds is a 1974 American documentary film about the Vietnam War directed by Peter Davis. The film's title is based on a quote from President Lyndon B. Johnson: "the ultimate victory will depend on the hearts and minds of the people who actually live out there". It won the Oscar for Best Documentary at the 47th Academy Awards presented in 1975.