The Birth of a Nation, originally called The Clansman, is a 1915 American silent epic drama film directed by D. W. Griffith and starring Lillian Gish. The screenplay is adapted from Thomas Dixon Jr.'s 1905 novel and play The Clansman. Griffith co-wrote the screenplay with Frank E. Woods and produced the film with Harry Aitken.

The Birth of a Nation is a landmark of film history, lauded for its technical virtuosity. It was the first non-serial American 12-reel film ever made. Its plot, part fiction and part history, chronicles the assassination of Abraham Lincoln by John Wilkes Booth and the relationship of two families in the Civil War and Reconstruction eras over the course of several years—the pro-Union (Northern) Stonemans and the pro-Confederacy (Southern) Camerons. It was originally shown in two parts separated by an intermission, and it was the first American-made film to have a musical score for an orchestra. It pioneered closeups and fadeouts, and it includes a carefully staged battle sequence with hundreds of extras (another first) made to look like thousands. It came with a 13-page "Souvenir Program". It was the first motion picture to be screened inside the White House, viewed there by President Woodrow Wilson, his family, and members of his cabinet.

The film was controversial even before its release, and it has remained so ever since; it has been called "the most controversial film ever made in the United States"^: 198 and "the most reprehensibly racist film in Hollywood history". Lincoln is nevertheless portrayed positively, albeit a friend of the South, atypical of a narrative that promotes the Lost Cause ideology. The film has been denounced for its racist depiction of African Americans. The film portrays blacks (many of whom are played by white actors in blackface) as unintelligent and sexually aggressive toward white women. The Ku Klux Klan (KKK) is portrayed as a heroic force, necessary to preserve American values, protect white women, and maintain white supremacy.

Popular among white audiences nationwide, the film's success was both a consequence of and a contributor to racial segregation throughout the U.S. In response to the film's depictions of black people and Civil War history, African Americans across the U.S. organized and protested. In Boston and other localities, black leaders and the NAACP spearheaded an unsuccessful campaign to have it banned on the basis that it inflamed racial tensions and could incite violence. Griffith's indignation at efforts to censor or ban the film motivated him to produce Intolerance the following year.

In spite of its divisiveness, The Birth of a Nation was a huge commercial success across the nation—grossing more than any previous motion picture—and it profoundly influenced both the film industry and American culture. The film has been acknowledged as an inspiration for the rebirth of the Ku Klux Klan, which took place only a few months after its release. In 1992, the Library of Congress deemed the film "culturally, historically, or aesthetically significant" and selected it for preservation in the National Film Registry.