The Richmond–Petersburg campaign was a series of battles around Petersburg, Virginia, fought from June 9, 1864, to March 25, 1865, during the American Civil War. Although it is more popularly known as the siege of Petersburg, it was not a classic military siege, in which a city is encircled with fortifications blocking all routes of ingress and egress, nor was it strictly limited to actions against Petersburg. The campaign consisted of nine months of trench warfare in which Union forces commanded by Lt. Gen. Ulysses S. Grant assaulted Petersburg unsuccessfully and then constructed trench lines that eventually extended over from the eastern outskirts of Richmond, Virginia, to around the eastern and southern outskirts of Petersburg. Petersburg was crucial to the supply of Confederate Gen. Robert E. Lee's army and the Confederate capital of Richmond. Numerous raids were conducted and battles fought in attempts to cut off the Richmond and Petersburg Railroad. Many of these battles caused the lengthening of the trench lines. Lee finally gave into the pressure and abandoned both cities in April 1865, leading to his retreat and surrender at Appomattox Court House. The siege of Petersburg foreshadowed the trench warfare that would be seen fifty years later in World War I, earning it a prominent position in military history. It also featured the war's largest concentration of African-American troops, who suffered heavy casualties at such engagements as the Battle of the Crater and Chaffin's Farm. Eastern Theater of the American Civil War In March 1864, Ulysses S. Grant was promoted to lieutenant general and was given command of the Union Army. He devised a coordinated strategy to apply pressure on the Confederacy from many points, something President Abraham Lincoln had urged his generals to do from the beginning of the war. Grant put Maj. Gen. William T. Sherman in immediate command of all forces in the West and moved his own headquarters to be with the Army of the Potomac (still commanded by Maj. Gen. George G.