Second+Manassas+Outcome

Union casualties were about 10,000 killed and wounded out of 62,000 engaged; the Confederates lost about 1,300 killed and 7,000 wounded out of 50,000. As the Union Army concentrated on Centreville, Lee planned his next move. He sent Jackson on another flanking march in an attempt to interpose his army between Pope and Washington. Pope countered the move and the two forces clashed a final time at the Battle of Chantilly(also known as Ox Hill) on September 1. Lee immediately began his next campaign on September 3, when the vanguard of the Army of Northern Virginia crossed the Potomac River, marching toward a fateful encounter with the Army of the Potomac in the Maryland Campaign and the Battle of Antietam.

Pope was relieved of command on September 12, 1862, and his army was merged into the Army of the Potomac as it marched into Maryland under McClellan. He spent the remainder of the war in the Department of the Northwest in Minnesota, dealing with the Dakota War of 1862. Pope sought scapegoats to spread the blame for his defeat. On November 25, 1862, Fitz John Porter was arrested and court-martialed for his actions on August 29. Porter was found guilty on January 10, 1863, of disobedience and misconduct, and he was dismissed from the Army on January 21. He spent most of the remainder of his life fighting against the verdict. In 1878, a special commission under General John M. Schofield exonerated Porter by finding that his reluctance to attack Longstreet probably saved Pope's Army of Virginia from an even greater defeat. Eight years later, President Chester A. Arthur reversed Porter's sentence.

James Longstreet was criticized for his performance during the battle and the postbellum advocates of the Lost Cause claimed that his slowness, reluctance to attack, and disobedience to Gen. Lee on August 29 were a harbinger of his controversial performance to come on July 2, 1863, at the Battle of Gettysburg. Lee's biographer, Douglas Southall Freeman, wrote: "The seeds of much of the disaster at Gettysburg were sown in that instant – when Lee yielded to Longstreet and Longstreet discovered that he would."