Almost everybody has some ineradicable impression of the past that was fabricated on a movie set. Whether it is the wounded at the Atlanta yards in Gone with the Wind or one of DeMille’s teeming sagas, movies have as much to do with how we envision the past as do, say, the photographs of Mathew Brady. The editors have culled stills from dozens of films to display the breadth of the cinematic history of the United States from Columbus (Fredric March) to Watergate (Robert Redford).