Gettysburg explains the battle's place in the Civil War, why two vast armies clashed there, and how, in the century and a half since, it has been re-imagined, re-created, and re-enacted. It is the story of a battle which no one planned but which became the bloodiest encounter of the war, and one with dramatically high stakes. The postwar romanticization of Gettysburg as the place of "might-have-beens" is based on a kernel of reality.

But it also suited the interests of both the winners and the losers for Gettysburg to become the Civil War in miniature: a glorious, storied, tragic tale small enough to comprehend, but large enough to be inspirational. If this was the battle that determined the war, Confederates could tell themselves that if only they had made different tactical choices, they would have won their independence, while Northerners could credit valor for their victory, without the unromantic need to invoke superior resources.

Yet there was only a war because of slavery, and Gettysburg's importance lies in its role in ending it. In the speech Abraham Lincoln gave there, four months after the battle, he expressed the hope that Union victory would inaugurate a "new birth of freedom." The history of the battle has been shaped by a contest over what that means.