American Civil War

On the eve of the war, the United States was deeply divided over slavery. The 1860 census counted nearly 4 million enslaved people, almost all in the Southern states, whose economy rested on cotton plantations, while the North was rapidly industrialising and urbanising. The dispute centred above all on the extension of slavery to the new western territories: the Missouri Compromise (1820), the Compromise of 1850, the Kansas-Nebraska Act (1854) and then the Supreme Court's Dred Scott decision (1857) only inflamed tensions. In November 1860, the young Republican Party, opposed to that extension, won the presidential election with Abraham Lincoln, without carrying a single Southern state.

South Carolina seceded as early as 20 December 1860, soon followed by six other states of the Deep South. Meeting in Montgomery, Alabama, delegates of the seceding states founded the Confederate States of America in February 1861 and chose Jefferson Davis as their president. On 12 April 1861, Confederate forces bombarded Fort Sumter in Charleston Harbor, whose federal garrison surrendered the next day. Lincoln called for 75,000 volunteers to put down the rebellion; four more slave states, including Virginia, then joined the Confederacy, which moved its capital to Richmond, while four border slave states, such as Kentucky and Maryland, remained in the Union. The two sides were unequal: the Union states had more than 20 million inhabitants and most of the industry and railways, the Confederacy about 9 million, of whom 3.5 million were enslaved.

The early years often went the South's way: its generals, led by Robert E. Lee, repelled Northern offensives in Virginia, from the First Battle of Bull Run (July 1861) to Chancellorsville (May 1863). The North nevertheless imposed a naval blockade on the Confederate coast and advanced down the Mississippi Valley under Ulysses S. Grant. At Antietam, on 17 September 1862, the bloodiest single-day battle of the war halted Lee's first invasion of the North and allowed Lincoln to announce the Emancipation Proclamation. Coming into force on 1 January 1863, it declared the enslaved people in rebel territory free and opened the federal army to Black soldiers, nearly 180,000 of whom would serve in it. In July 1863, Lee's defeat at Gettysburg, Pennsylvania, and Grant's capture of Vicksburg, which split the Confederacy in two, marked the turning point of the conflict.

Appointed commander of all the Union armies in 1864, Grant waged a war of attrition against Lee in Virginia, while William T. Sherman took Atlanta on 2 September, then marched across Georgia to the sea, destroying the South's resources. These successes secured Lincoln's re-election in November 1864. On 31 January 1865, the House of Representatives in turn passed the constitutional amendment abolishing slavery, already approved by the Senate. After the fall of Richmond, the encircled Lee surrendered at Appomattox on 9 April 1865, and the last Confederate armies laid down their arms in the following weeks. On 14 April, Lincoln was fatally shot by John Wilkes Booth, an actor sympathetic to the South, at Ford's Theatre in Washington; he died the next day.

The deadliest conflict in the history of the United States, the Civil War cost the lives of 620,000 soldiers according to the traditional estimate, and of nearly 750,000 according to a demographic study published in 2011; around two-thirds of them died of disease. It established the supremacy of the federal government over the states and the lasting unity of the country. The amendment abolishing slavery was ratified on 6 December 1865, and two further amendments granted citizenship to former slaves (1868) and prohibited denying the right to vote on grounds of race (1870). But after the Reconstruction era, which ended in 1877, the Southern states imposed racial segregation and stripped most Black people of the vote, a situation that only the civil rights movement would challenge, nearly a century later.