History: American Civil War (1861-1865)

Eastern theater 1861–1863
Because of the fierce resistance of a few initial Confederate forces at Manassas, Virginia, in July 1861, a march by Union troops under the command of Maj. Gen. Irvin McDowell on the Confederate forces there was halted in the First Battle of Bull Run, or First Manassas, McDowell's troops were forced back to Washington, D.C., by the Confederates under the command of Generals Joseph E. Johnston and P. G. T. Beauregard. It was in this battle that Confederate General Thomas Jackson received the nickname of "Stonewall" because he stood like a stone wall against Union troops.
Alarmed at the loss, and in an attempt to prevent more slave states from leaving the Union, the U.S. Congress passed the Crittenden-Johnson Resolution on July 25 of that year, which stated that the war was being fought to preserve the Union and not to end slavery.
Maj. Gen. George B. McClellan took command of the Union Army of the Potomac on July 26 (he was briefly general-in-chief of all the Union armies, but was subsequently relieved of that post in favor of Maj. Gen. Henry W. Halleck), and the war began in earnest in 1862. Upon the strong urging of President Lincoln to begin offensive operations, McClellan attacked Virginia in the spring of 1862 by way of the peninsula between the York River and James River, southeast of Richmond. Although McClellan's army reached the gates of Richmond in the Peninsula Campaign, Johnston halted his advance at the Battle of Seven Pines, then General Robert E. Lee and top subordinates James Longstreet and Stonewall Jackson defeated McClellan in the Seven Days Battles and forced his retreat. The Northern Virginia Campaign, which included the Second Battle of Bull Run, ended in yet another victory for the South. McClellan resisted General-in-Chief Halleck's orders to send reinforcements to John Pope's Union Army of Virginia, which made it easier for Lee's Confederates to defeat twice the number of combined enemy troops.