This film is indespensible in Hollywood history. This is the birth of the modern feature-length film, although it is a terribly troubled birth. The first half of the film, what President Woodrow Wilson described as "watching history by flashes of ligthening," is a glimpse into the American Civil War, albeit from the Southern point of view, created at a time when the old veterans still walked the earth, and they approved of this message. It is as close as the Civil War can ever get to "Band of Brothers," "Platoon," or the opening minutes of "Saving Private Ryan." It's 110 years old, so it lacks the polish of those films, but has the veracity. Compare the lean, lithe soldiers in the battle scenes of this film to the pudgy, soft-cheeked reanactors of "Gettysburg" from the 1990s and you'll know its a glimpse of living history.
The second half of the film is where Griffith went too far, and it's where the worst racist tropes of the film come to life as the KKK comes charging in, with the first sight of a long-lasting cinematic cavalry tradtion, to save the day. Even at the worst moments it's still an open window into the past. The average African American finds these scenes atrocious, but it is for all its racist pandering still a visual record of the attitudes faced by African Americans in that time. One can see, and feel, what the Black community must have felt in 1915.
This is not something everyone should watch. It's cinematic history and even beyond the larger faults, it is guilty of the tripe and corn that passed for entertainment at the time. Only people who have spent time with other silent films (or perhaps a stray Civil War buff) is going to be able to sit through this, or get much out of it. D.W. Griffith, for good or evil, created the cinematic world that John Ford, Howard Hawks, and William Wellman entered, and these latter guys were among those who passed American film into the hands of Spielberg and Scorcese. It is impossible to banish D.W. Griffith from film history, and the movie does what we ask historical films to do, it captures a time and a place and attitudes that existed. I would never recommend this movie without a massive abundance of caution, but it is a living time trip to 1865 and 1915.