A civil war fought in the United States of America between the northern states, popularly referred to as the "Union", and the seceding southern states (in the U.S., the South), calling themselves the Confederate States of America or the "Confederacy". The causes of the war included state's rights versus federal rights, economic and cultural differences but mainly, slavery.
The war is also known in the South as the War Between the States or (now half-humorously) as The War of Northern Aggression.
The states which seceded consisted of Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas and Virginia. Several 'slave states' did not secede: Delaware, Maryland, Kentucky, and Missouri. Although Kentucky did not secede, it declared itself neutral in the conflict. The state of West Virginia was created by the secession of the northwestern counties of Virginia from the state of Virginia.
It began in 12 April 1861 when Confederate forces opened fire on Fort Sumter in the harbor of Charleston, South Carolina. A near-immediate march by Union troops on the Confederate capital of Richmond, Virginia, was halted in the First Bull Run, whereupon they were forced back to Washington, D.C. by Confederate troops under the command of General P G T Beauregard. General George McClellan took control of the Union armies, and the war began in earnest in 1862.
After his defeat in The Seven Days and his inability to engage Confederate troops after his victory at Antietam, McClellan was replaced by General Ambrose Burnside. Burnside suffered near-immediate defeat at the battle of Fredricksburg, and was replaced by General Joseph Hooker. Hooker, too, proved unable to defeat the enemy, and was relieved after the disastrous battle of Chancellorsville. He was replaced by General George Meade, who started to make progress after winning a victory at Gettysburg.
While the Confederate forces had marked success in the Eastern theater, fortune did not smile upon them in the West. Confederate forces were driven from Missouri early in the war, holding that key strategic state for the Union. Nashville fell. The Mississippi was opened up to Vicksburg with the taking of Island No. 10 and New Madrid, Missouri and then Memphis. New Orleans was captured in 1862 allowing the Union forces to begin moving up the Mississippi as well.
The Union's key tactician was Ulysses S. Grant, who won victories at Fort Donelson, Shiloh, and Vicksburg, Mississippi, and was able to drive the confederacy out of Tennessee. Grant understood the concept of total war and realized that only the utter defeat of Confederate forces would bring an end to the war. At the beginning of 1864, Grant was given control of all the Union armies. He chose to make his headquarters with The Army of the Potomac although Meade remained the actual commander of that particular army. Union forces in the East faced a setback at the Wilderness and took large amounts of casualties at Spotsylvania and Cold Harbor but Grant was tenacious and kept pressing the Army of Northern Virginia under the command of Robert E. Lee. He slowly ground down the Confederate armies; he laid siege to their forces in the siege of Petersburg while General William Sherman marched on Atlanta and laid waste to much of the rest of Georgia.
The war ended in April 1865 with the surrender of Confederate forces. Lee surrendered his Army of Northern Virginia on 9 April 1865 at Appomattox Court house. J.E. Johnson, who was in charge of the army in North Carolina, surrendered his troops to Sherman shortly thereafter.
Major battles included First Bull Run, Second Bull Run, Shiloh, The Seven Days, Antietam, Vicksburg, Gettysburg, and the siege of Petersburg. The most significant naval battle was between the Monitor and the CSS Virginia, which is often claimed to be the first modern naval battle.
This war ended with the emancipation of all slaves and a great deal of ill-will among the Southern survivors. Slaves were not universally freed until the passage of the Thirteenth Amendment to the Constitution by 3/4 of the states, which did not occur until December of 1865, 8 months after the end of the war.