>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" and "the most reprehensibly racist film in Hollywood history." The film has been denounced for its racist depiction of African Americans. The film portrays its black characters (many of whom are played by white actors in blackface) as unintelligent and sexually aggressive toward white women. The Ku Klux Klan (KKK), a white supremacist far-right hate group, is portrayed as a heroic force that protects white women and maintains white supremacy.

(from Wikipedia: https://en.wikipedia.org/wiki/The_Birth_of_a_Nation)