D.W. Griffith's Birth of a Nation is no doubt a long film, but it's also very important in film history. It covers two story lines: 1) the United States Civil War and 2) Reconstruction. Both follow the Stoneman family in one way or another.
Looking back, viewers should have no doubt that Griffith's Birth of a Nation is racist. However, upon release, the film received rave reviews from a number of people (except groups like the NAACP, who boycotted the film and called for it to be banned) and made a tremendous amount of money. On movie review aggregator RottenTomatoes.com, it holds a critics approval rating of 98% but an audience approval rating of 56%. Reads that sites critical consensus: "Racial depictions aside, The Birth of a Nation is a landmark film whose achievements and pioneering techniques remain fully relevant today."
On a budget of less than $100,000, it is estimated it made back between $50 and $100 million at the box office. Also, in 1992, the film was selected for preservation in the National Film Registry and was the first film ever shown in the White House (to President Woodrow Wilson). Film historian Kevin Brownlow noted that "[there are] so many advances in film-making technique."
However, Birth of a Nation was credited with reviving the KKK and being an instrumental part in helping everyday Americans to accept the organization. Griffith later made a follow-up in 1916 called Intolerance.