The Battle of Antietam, which took place on September 17, 1862, remains the single bloodiest day in America’s history. As a turning point in the Civil War, the narrow Union victory was the key catalyst for Lincoln to issue his Emancipation Proclamation. Yet Antietam was not only a battle that dramatically changed the fortunes and meaning of the war; it also changed America in ways we feel today. Antietam ushered in a new beginning in politics, military strategy, gender roles, battlefield medicine, war photography, and the values and worldview of the postwar generation. A masterful and fine-grained account of the battle and the intimate experiences of those who were there, Stephen Budiansky’s A Day in September expands this view to encompass Antietam’s enduring legacy in American society and culture.