The American Civil War (1861–1865) was a major war between the United States (the "Union") and eleven Southern states which declared that they had a right to secession and formed the Confederate States of America, led by President Jefferson Davis. The Union, led by President Abraham Lincoln and the Republican Party, which had opposed the expansion of slavery[1][2][3] into territories owned by the United States, rejected any right of secession. Fighting commenced on April 12, 1861, when Confederate forces attacked a United States (federal) military installation at Fort Sumter in South Carolina, the first state to secede.

During the first year, the Union assumed control of the border states and established a naval blockade as both sides raised large armies. In 1862 large, bloody battles such as Shiloh and Antietam were fought, causing massive casualties unprecedented in U.S. military history largely as a result of incompatibility between new weapons and old battlefield tactics. In September 1862, Lincoln's Emancipation Proclamation made the freeing of slaves in the South a war goal and gave a higher moral cause to the war, despite opposition from northern Copperheads who tolerated secession and slavery. Emancipation reduced the likelihood of intervention from Britain and France on behalf of the Confederacy. In addition, the goal also allowed the Union to recruit African-Americans for reinforcements, a resource that the Confederacy did not dare exploit until it was too late. The border states and War Democrats reluctantly accepted emancipation as part of total war needed to save the Union. In the East, Confederate general Robert E. Lee assumed command of the Army of Northern Virginia and rolled up a series of victories over the Army of the Potomac, but his best general, Thomas Jonathan "Stonewall" Jackson, was killed at the Battle of Chancellorsville in May 1863. Lee's invasion of the North was repulsed at the Battle of Gettysburg in Pennsylvania in July 1863; he barely managed to escape back to Virginia. The Union Navy captured the port of New Orleans in 1862, and Ulysses S. Grant seized control of the Mississippi River by capturing Vicksburg, Mississippi in July 1863, thus splitting the Confederacy.

By 1864, long-term Union advantages in geography, manpower, industry, finance, political organization and transportation were overwhelming the Confederacy. Grant fought a number of bloody battles with Lee in Virginia in the summer of 1864...