The Confederate States of America (CSA), commonly referred to as the Confederate States or simply the Confederacy, was an unrecognized breakaway republic in North America that existed from February 8, 1861, to May 9, 1865. The Confederacy comprised U.S. states that declared secession and warred against the United States (the Union) during the American Civil War. Eleven U.S. states, nicknamed Dixie, declared secession and formed the main part of the CSA. They were South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, Tennessee, and North Carolina. Kentucky and Missouri also had declarations of secession and full representation in the Confederate Congress during their Union army occupation.

The Confederacy was formed on February 8, 1861, by seven slave states: South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas. All seven of the states were located in the Deep South region of the United States, whose economy was heavily dependent upon agricultureparticularly cottonand a plantation system that relied upon enslaved Americans of African descendent for labor. Convinced that white supremacy and slavery were threatened by the November 1860 election of Republican candidate Abraham Lincoln to the U.S. presidency, on a platform which opposed the expansion of slavery into the western territories, the Confederacy declared its secession from the United States, with the loyal states becoming known as the Union during the ensuing American Civil War. In the Cornerstone Speech, Confederate Vice President Alexander H. Stephens described its ideology as centrally based "upon the great truth that the negro is not equal to the white man; that slavery, subordination to the superior race, is his natural and normal condition."Before Lincoln took office on March 4, 1861, a provisional Confederate government was established on February 8, 1861. It was considered illegal by the United States federal government, and Northerners thought of the Confederates as traitors. After war began in April, four slave states of the Upper SouthVirginia, Arkansas, Tennessee, and North Carolinaalso joined the Confederacy. The Confederacy later accepted the slave states of Missouri and Kentucky as members, accepting rump state assembly declarations of secession as authorization for full delegations of representatives and senators in the Confederate Congress; they were never substantially controlled by Confederate forces, despite the efforts of Confederate shadow governments, which were eventually expelled. The Union rejected the claims of secession as illegitimate.

The Civil War began on April 12, 1861, when the Confederates attacked Fort Sumter, a Union fort in the harbor of Charleston, South Carolina. No foreign government ever recognized the Confederacy as an independent country, although Great Britain and France granted it belligerent status, which allowed Confederate agents to contract with private concerns for weapons and other supplies. By 1865, the Confederacy's civilian government dissolved into chaos: the Confederate States Congress adjourned sine die, effectively ceasing to exist as a legislative body on March 18. After four years of heavy fighting, nearly all Confederate land and naval forces either surrendered or otherwise ceased hostilities by May 1865. The war lacked a clean end, with Confederate forces surrendering or disbanding sporadically throughout most of 1865. The most significant capitulation was Confederate general Robert E. Lee's surrender to Ulysses S. Grant at Appomattox on April 9, after which any doubt about the war's outcome or the Confederacy's survival was extinguished, although another large army under Confederate general Joseph E. Johnston did not formally surrender to William T. Sherman until April 26. Contemporaneously, President Lincoln was assassinated by Confederate sympathizer John Wilkes Booth on April 15. Confederate President Jefferson Davis's administration declared the Confederacy dissolved on May 5, and acknowledged in later writings that the Confederacy "disappeared" in 1865. On May 9, 1865, U.S. president Andrew Johnson officially called an end to the armed resistance in the South.

After the war, Confederate states were readmitted to the Congress during the Reconstruction era, after each ratified the 13th Amendment to the U.S. Constitution outlawing slavery. Lost Cause ideology, an idealized view of the Confederacy valiantly fighting for a just cause, emerged in the decades after the war among former Confederate generals and politicians, as well as organizations such as the United Daughters of the Confederacy and the Sons of Confederate Veterans. Intense periods of Lost Cause activity developed around the time of World War I, and during the civil rights movement of the 1950s and 1960s in reaction to growing support for racial equality. Advocates sought to ensure future generations of Southern whites would continue to support white supremacist policies such as the Jim Crow laws through activities such as building Confederate monuments and influencing textbooks to portray the Confederacy in a favorable light. The modern display of Confederate flags primarily started during the 1948 presidential election, when the battle flag was used by the Dixiecrats, who opposed the Civil Rights Movement; more recently, segregationists have continued the practice, using it for demonstrations.

The American Civil War (April 12, 1861 – May 9, 1865; also known by other names) was a civil war in the United States between the Union (states that remained loyal to the federal union, or "the North") and the Confederacy (states that voted to secede, or "the South"). The central cause of the war was the status of slavery, especially the expansion of slavery into territories acquired as a result of the Louisiana Purchase and the Mexican–American War. On the eve of the Civil War in 1860, four million of the 32 million Americans (~13%) were enslaved black people, almost all in the South.The practice of slavery in the United States was one of the key political issues of the 19th century. Decades of political unrest over slavery led up to the Civil War. Disunion came after Abraham Lincoln won the 1860 United States presidential election on an anti-slavery expansion platform. An initial seven southern slave states declared their secession from the country to form the Confederacy. Confederate forces seized federal forts within territory they claimed. The last-minute Crittenden Compromise tried to avert conflict but failed; both sides prepared for war. Fighting broke out in April 1861 when the Confederate army began the Battle of Fort Sumter in South Carolina, just over a month after the first inauguration of Abraham Lincoln. The Confederacy grew to control at least a majority of territory in eleven states (out of the 34 U.S. states in February 1861), and asserted claims to two more. Both sides raised large volunteer and conscription armies. Four years of intense combat, mostly in the South, ensued.

During 1861–1862 in the war's Western Theater, the Union made significant permanent gains—though in the war's Eastern Theater the conflict was inconclusive. On January 1, 1863, Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal, declaring all persons held as slaves in states in rebellion "forever free." To the west, the Union destroyed the Confederate river navy by the summer of 1862, then much of its western armies, and seized New Orleans. The successful 1863 Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Confederate General Robert E. Lee's incursion north ended at the Battle of Gettysburg. Western successes led to General Ulysses S. Grant's command of all Union armies in 1864. Inflicting an ever-tightening naval blockade of Confederate ports, the Union marshaled resources and manpower to attack the Confederacy from all directions. This led to the fall of Atlanta in 1864 to Union General William Tecumseh Sherman and his march to the sea. The last significant battles raged around the ten-month Siege of Petersburg, gateway to the Confederate capital of Richmond.

The Civil War effectively ended on April 9, 1865, when Confederate General Lee surrendered to Union General Grant at the Battle of Appomattox Court House, after Lee had abandoned Petersburg and Richmond. Confederate generals throughout the Confederate army followed suit. The conclusion of the American Civil War lacks a clean end date: land forces continued surrendering until June 23. By the end of the war, much of the South's infrastructure was destroyed, especially its railroads. The Confederacy collapsed, slavery was abolished, and four million enslaved black people were freed. The war-torn nation then entered the Reconstruction era in a partially successful attempt to rebuild the country and grant civil rights to freed slaves.

The Civil War is one of the most studied and written about episodes in the history of the United States. It remains the subject of cultural and historiographical debate. Of particular interest is the persisting myth of the Lost Cause of the Confederacy. The American Civil War was among the earliest to use industrial warfare. Railroads, the telegraph, steamships, the ironclad warship, and mass-produced weapons saw wide use. In total the war left between 620,000 and 750,000 soldiers dead, along with an undetermined number of civilian casualties. President Lincoln was assassinated just five days after Lee's surrender. The Civil War remains the deadliest military conflict in American history. The technology and brutality of the Civil War foreshadowed the coming World Wars.