The plot of The Birth of a Nation revolves around two families living on either side of the Mason-Dixon Line who become friends when their sons board together at school. The Stonemans, the Northern family, live in Washington, D.C., and own a rural getaway in Pennsylvania. The Honorable Austin Stoneman, an abolitionist politician, presides over his family, which includes a delicate daughter named Elsie, a dandy prankster named Phil, and a younger brother named Tod. The Camerons, the Southern family, preside over a modest but idyllic plantation in Piedmont, South Carolina, where slaves pick cotton in satisfaction and happily dance to entertain their masters. Margaret is the refined older sister, while Flora, the younger sister, is dreamy and innocent. Of the three Cameron brothers, Ben develops into the main character, defending the South’s ideals at all costs. His two younger brothers are Wade and Duke.
The film is divided roughly into halves, with subsections drawing from a historical chronology of the Civil War. After an initial prologue that blames the Civil War and Reconstruction on the introduction of Africans to America, the Stoneman boys travel south during the antebellum period to visit their old pals. Romances develop: Phil falls for Margaret, and Ben falls for a daguerreotype of Elsie. Ben carries this picture of Elsie with him until he finally meets her. Later, Dr. Cameron reads his family a newspaper article stating that the South will secede from the Union if the North carries the next elections. After the Stonemans leave, war breaks out, interrupting relations between the families. One of Griffith’s historical facsimiles, or fictional documentations of actual events (which will later include General Lee’s surrender and Lincoln’s assassination), shows Lincoln signing for the first wave of volunteers.
Epic battles follow, spanning three years and showing the devastation the war wrecks throughout the country, especially in the South. Exceptionally produced battle sequences focus on both personal details and the bloody scale of the depredation. First, a festive Piedmont ball celebrates the South’s early victory at Bull Run, and so the three Cameron brothers head off to fight in good spirits. Griffith then spans two and a half years with one cut, and Ben, battle-worn and still in the field, reads letters from home. A predominantly black militia ransacks the defenseless Cameron home, while Ben dreams of Elsie. Tragically, the two youngest sons of each family, Tod and Duke, suffer fatal wounds at the same moment on the battlefield, dying in each other’s arms. General Sherman begins his infamous march, destroying Georgia as he moves forward. Wade Cameron dies in Atlanta, and the Union succeeds in pinching off what’s left of the Confederacy’s meager food supply.
As the drama heightens, the two oldest brothers meet in battle. Though Ben’s undermanned, underfed, and ravaged platoon cannot possibly win, he heroically upholds the honor of the South. Risking his life and suffering a head wound, he maniacally sprints to the Union trench and jams a Confederate flag down the gullet of a cannon. Retreating to his own trench, he again risks his life to save a wounded Union soldier while Phil’s troops cheer. Eventually taken to a Union hospital in Washington, D.C., Ben finally meets Elsie, who is volunteering there. Mrs. Cameron travels to visit Ben and, upon learning he has been condemned to death under a bogus charge of spying, personally appeals to President Lincoln, who graciously pardons Ben. On April 9, 1865, Lee surrenders to Grant, and Ben leaves for home. He returns to find his home in disrepair, with little food and all the good clothing sold. He embraces Flora. Meanwhile, the elder Stoneman tries to convince Lincoln to rule mercilessly over the vanquished South, but Lincoln refuses, preferring instead diplomatic restitution. Five days later, Lincoln is assassinated at Ford’s Theater, a historical event that in this movie is witnessed by Phil and Elsie Stoneman, who are at the theater that night. The Camerons deeply mourn the loss of their “best friend,” and Stoneman assumes power, ending the first part of the film on a decidedly bleak and somber note.
In Griffith’s version of the postwar era, all blacks who aren’t “faithful souls” team up with carpetbaggers from the North to loot, pillage, and degrade the time-honored traditions of Southern culture. Stoneman, a champion of black equality in the South, forces Senator Charles Sumner (a historical figure) to acknowledge the legitimacy of Stoneman’s mulatto protégé, Silas Lynch, who secretly lusts after Elsie and is sent down to organize the emancipated slaves. Headquartered in Piedmont, Lynch instigates former slaves to rise up against Southern whites in vengeance, teams effectively with the carpetbaggers, and essentially oversees mob rule. Stoneman, in ill health, visits, bringing Elsie with him. Ben refuses to shake Lynch’s hand. The two pairs of interfamily lovebirds try to restart their romances with genteel garden walks, but memories of the war make reuniting difficult. Margaret imagines a picture of Wade laid waste on a battlefield and can no longer speak to Phil. Silas Lynch spies on Ben and Elsie, who eventually succumb to their love.
In response to a horrific Election Day in which Lynch’s black supremacists intimidate the whites on the streets and in the South Carolina legislature, Ben searches his soul and finds inspiration in white children frightening black children by pretending to be ghosts and hiding under white sheets. The Ku Klux Klan is born. Southern women secretly make hundreds of thousands of uniforms bearing a woven St. Andrews Cross, and the “Night Riders” start a new war against Lynch’s militia. Ben’s involvement in the Klan crushes Elsie, but she does not sell him out. Flora consoles Elsie and then skips off into the woods to fetch water from a spring. There, Gus, a newly promoted black officer, approaches Flora and proffers marriage. Flora slaps him, and Gus begins to chase her through the forest. Ben follows behind in search of Flora, having been told of her errand. Gus reassures Flora that he intends her no harm, but Flora finds herself pinned on the edge of a cliff. Threatening to jump rather than be touched by Gus, she either accidentally falls or intentionally jumps off the cliff, where shortly after she dies in Ben’s arms. A search commences for the fearful Gus. After a complex chase sequence, the Klan eventually catches Gus and lynches him. They dump his body at Silas Lynch’s door.
When Lynch discovers the body the next morning, the film’s climax begins. The black militia with its white sympathizers fight against the Klan. Some of the Camerons are captured, but they are freed by faithful blacks. In flight, Dr. Cameron, Phil, and Margaret come across a tiny shack in the woods owned by Union veterans, who invite them in and make peace with the Camerons over their common hatred for renegade blacks. Elsie runs to Lynch for help, but he tries to force her to marry him, promising to make her queen of his “Black Empire.” When Austin Stoneman interrupts, Lynch confides to him that he wants to marry his daughter. Exposing his own hypocrisy, Stoneman is repulsed. The noble and well-supported Klan begins its lengthy and heroic mission to rescue Elsie and the group in the cabin, now besieged by the black militia. The Klan triumphs in both battles, saving one Union veteran the horror of bashing his own child’s head to save the child from the black militia. Both couples are restored and united in marriage, white supremacists strip power from blacks through intimidation tactics, and, in a religious coda meant to symbolize the second coming of the “Prince of Peace,” Jesus and his angels in the City of God stand in approval over the scene.