The American Civil War was a civil war in the United States of America. Eleven Southern slave states declared their secession from the U.S., formed the Confederate States of America and fought against the U.S. federal government.

Hostilities began on April 12, 1861, when Confederate forces attacked a U.S. military installation at Fort Sumter in South Carolina. In the war's first year, the Union assumed control of the border states and established a naval blockade as both sides massed armies and resources. In 1862, battles such as Shiloh and Antietam caused massive casualties unprecedented in U.S. military history.

In the East, Confederate commander Robert E. Lee won a series of victories, but Lee's loss at Gettysburg in July, 1863 proved the turning point. Union commander Ulysses S. Grant fought bloody battles of attrition with Lee in 1864, forcing Lee to defend the Confederate capital at Richmond, Virginia. Union general William Sherman captured Atlanta, Georgia, and began his famous March to the Sea. Confederate resistance collapsed after Lee surrendered to Grant at Appomattox on April 9, 1865.

The war caused 620,000 soldier deaths and an undetermined number of civilian casualties, ended slavery in the United States, restored the Union and strengthened the role of the federal government.