American Civil War: Robert E. Lee resigns his commission in the United States Army in order to command the forces of the state of Virginia.

Robert Edward Lee (January 19, 1807 October 12, 1870) was a Confederate general who served the Confederate States of America in the American Civil War, during which he was appointed the overall commander of the Confederate States Army. He led the Army of Northern Virginia, the Confederacy's most powerful army, from 1862 until its surrender in 1865. During the war, Lee earned a solid reputation as a skilled tactician, for which he was revered by his officers and men as well as respected and feared by his adversaries in the Union Army.

A son of Revolutionary War officer Henry "Light Horse Harry" Lee III, Lee was a top graduate of the United States Military Academy and an exceptional officer and military engineer in the United States Army for 32 years. During this time, he served throughout the United States, distinguished himself during the MexicanAmerican War, and served as Superintendent of the United States Military Academy. Lee married Mary Anna Custis Lee, great-granddaughter of George Washington's wife Martha. When Virginia's 1861 Richmond Convention declared secession from the Union, Lee chose to follow his home state, despite his desire for the country to remain intact and an offer of a senior Union command. During the first year of the Civil War, he served in minor combat operations and as a senior military adviser to Confederate President Jefferson Davis.

Lee took command of the Army of Northern Virginia in June 1862 during the Peninsula Campaign following the wounding of Joseph E. Johnston. He succeeded in driving the Union Army of the Potomac under George B. McClellan away from the Confederate capital of Richmond during the Seven Days Battles, although he was unable to destroy McClellan's army. Lee then overcame Union forces under John Pope at the Second Battle of Bull Run in August. His invasion of Maryland that September ended with the inconclusive Battle of Antietam, after which he retreated to Virginia. Lee then won two decisive victories at Fredericksburg and Chancellorsville before launching a second invasion of the North in the summer of 1863, where he was decisively defeated at the Battle of Gettysburg by the Army of the Potomac under George Meade. He led his army in the minor and inconclusive Bristoe Campaign that fall before General Ulysses S. Grant took command of Union armies in the spring of 1864. Grant engaged Lee's army in bloody but inconclusive battles at the Wilderness and Spotsylvania before the lengthy Siege of Petersburg, which was followed in April 1865 by the capture of Richmond and the destruction of most of Lee's army, which he finally surrendered to Grant at Appomattox Court House.

In 1865, Lee became president of Washington College (later Washington and Lee University) in Lexington, Virginia; in that position, he supported reconciliation between North and South. Lee accepted "the extinction of slavery" provided for by the Thirteenth Amendment, but opposed racial equality for African Americans. After his death in 1870, Lee became a cultural icon in the South and is largely hailed as one of the Civil War's greatest generals. As commander of the Army of Northern Virginia, he fought most of his battles against armies of significantly larger size, and managed to win many of them. Lee built up a collection of talented subordinates, most notably James Longstreet, Stonewall Jackson, and J. E. B. Stuart, who along with Lee were critical to the Confederacy's battlefield success. In spite of his success, his two major strategic offensives into Union territory both ended in failure. Lee's aggressive and risky tactics, especially at Gettysburg, which resulted in high casualties at a time when the Confederacy had a shortage of manpower, have come under criticism.

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.