Abraham Lincoln's victory in the 1860 election saw the secession of eleven states from the Union, and the formation of the Confederate States of America. Five border states remained neutral throughout the war, however their citizens enlisted in both armies, which occasionally saw family members opposing one another on the battlefield. By 1862, both forces developed into two of the most advanced armies in the world; these developments were reflected in the increased ferocity and scale of the battles as the war progressed, such as Antietam and Shiloh.
General Robert E. Lee took command of the Army of Northern Virginia in 1862, and used his tactical prowess and leadership skills to hold the southern border against (predominantly larger) Union forces. It was at this time that Ulysses S. Grant also emerged as the most successful General in the Union Army. Following Grant's decisive victories in the Vicksburg Campaign, Lee focused the Confederacy's attacks on the eastern front. After victory at Chancellorsville, Lee invaded the North, but his forces were met by General George Meade's Army of the Potomac at the Battle of Gettysburg. This was a decisive victory for the Union, but was the costliest battle of the war, and is seen by many as the war's turning point.
Following his victories in the Chattanooga campaign, Grant was promoted to Lieutenant General, and then focused his attention on defeating Lee. In 1864, Grant's Overland Campaign pushed Lee's forces back through Virginia, at great cost to both sides. It was at this time that the Union's superior manpower, resources and mobility proved decisive in determining the war's outcome. The Union army was able to replace their casualties with new conscripts, due to a higher population, and their financial reserves meant they could afford to pay recruits more than their opponents. Grant's war of attrition, and heavy losses at battles such as the Wilderness and Spotsylvania, caused many disheartened Confederates to desert. By early 1865, the Confederate cause was lost, and on April 9, General Robert E. Lee surrendered to Ulysses S. Grant, effectively ending the war.
Five days later, as part of a wider conspiracy to assassinate the Union leadership, President Lincoln was shot and assassinated by John Wilkes Booth. The assassination was met with condemnation from many Confederate leaders, and cast a shadow over the nation's relief at the war's ending. Vice President Andrew Johnson then ascended to the presidency, before Ulysses S. Grant was elected in 1868. A period of Reconstruction followed until 1877, however, the legacy of the war and slavery continue to be felt today. Nationwide emancipation was achieved on December 6, 1865, though most African Americans (particularly in the South) saw no progress beyond this until the civil rights movement in the 1950s and 1960s, while racial inequalities continue to be reflected in the U.S. socioeconomic landscape.