The American Civil War was a pivotal conflict between the Northern Union and the Southern Confederacy, primarily fought over slavery, states’ rights, and federal authority. Triggered by the election of Abraham Lincoln and the secession of eleven Southern states, the war resulted in over 600,000 deaths and remains the deadliest conflict in U.S. history. Major battles such as Gettysburg and Antietam shaped the outcome, leading to Union victory, the preservation of the United States, and the passage of the 13th Amendment abolishing slavery. The Civil War fundamentally transformed the nation’s political structure, economy, and civil rights landscape, laying the groundwork for Reconstruction and modern America.