The Emancipation Proclamation, officially Proclamation 95, was a presidential proclamation and executive order issued by United States President Abraham Lincoln on January 1, 1863, during the Civil War. The Proclamation changed the legal status of more than 3.5 million enslaved African Americans in the secessionist Confederate states from enslaved to free. As soon as a slave escaped the control of his or her owner, either by running away across Union lines or through the advance of federal troops, the person was permanently free. In addition, the Proclamation allowed for the recruitment of former slaves into the paid service of the United States armed forces.

On September 22, 1862, Lincoln issued the preliminary Emancipation Proclamation. Its third paragraph reads:

That on the first day of January, in the year of our Lord, one thousand eight hundred and sixty-three, all persons held as slaves within any State or designated part of a State, the people whereof shall then be in rebellion against the United States, shall be then, thenceforward, and forever free; and the Executive Government of the United States, including the military and naval authority thereof, will recognize and maintain the freedom of such persons, and will do no act or acts to repress such persons, or any of them, in any efforts they may make for their actual freedom.

On January 1, 1863, Lincoln issued the final Emancipation Proclamation. After quoting from the preliminary Emancipation Proclamation, it stated:

I, Abraham Lincoln, President of the United States, by virtue of the power in me vested as Commander-in-Chief, of the Army and Navy of the United States in time of actual armed rebellion against authority and government of the United States, and as a fit and necessary war measure for suppressing said rebellion, do ... order and designate as the States and parts of States wherein the people thereof respectively, are this day in rebellion, against the United States, the following, towit:

Lincoln then listed the ten states still in rebellion, excluding parts of states under Union control, and continued:

I do order and declare that all persons held as slaves within said designated States, and parts of States, are, and henceforward shall be free.... [S]uch persons of suitable condition, will be received into the armed service of the United States.... And upon this act, sincerely believed to be an act of justice, warranted by the Constitution, upon military necessity, I invoke the considerate judgment of mankind, and the gracious favor of Almighty God....

The proclamation was directed to all of the areas in rebellion and all segments of the executive branch (including the Army and Navy) of the United States. It proclaimed the freedom of enslaved people in the ten states in rebellion. Even though it excluded areas not in rebellion, it still applied to more than 3.5 million of the 4 million enslaved people in the country. Around 25,000 to 75,000 were immediately emancipated in those regions of the Confederacy where the US Army was already in place. It could not be enforced in the areas still in rebellion, but, as the Union army took control of Confederate regions, the Proclamation provided the legal framework for the liberation of more than three and a half million enslaved people in those regions through the end of the war. The Emancipation Proclamation outraged white Southerners and their sympathizers, who saw it as the beginning of a race war. It energized abolitionists, and undermined those Europeans who wanted to intervene to help the Confederacy. The Proclamation lifted the spirits of African Americans both free and enslaved; it led many to escape from their masters and get to Union lines to obtain their freedom and to join the Union Army. The Emancipation Proclamation became a historic document because it "would redefine the Civil War, turning it from a struggle to preserve the Union to one focused on ending slavery, and set a decisive course for how the nation would be reshaped after that historic conflict."The Emancipation Proclamation was never challenged in court. To ensure the abolition of slavery in all of the U.S., Lincoln also insisted that Reconstruction plans for Southern states require them to enact laws abolishing slavery (which occurred during the war in Tennessee, Arkansas, and Louisiana); Lincoln encouraged border states to adopt abolition (which occurred during the war in Maryland, Missouri, and West Virginia) and pushed for passage of the Thirteenth Amendment. The Senate passed the 13th Amendment by the necessary two-thirds vote on April 8, 1864; the House of Representatives did so on January 31, 1865; and the required three-fourths of the states ratified it on December 6, 1865. The amendment made slavery and involuntary servitude unconstitutional, "except as a punishment for crime."

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.