In short, this battle was one of the largest battles of the civil war with around 200,000 soldiers involved. There were 120,000 union troops to Lee's 80,000 confederate army. The union let by a newly appointed commander Ambrose Burnside, staged an attack across the Rappahannock River on both sides of Lee's army, the confederates held strong and were able to move out before the union bulk could arrive and eventually the union forces retreated after massive casualities (13,000ish union to 5,000 for the Grey coats). The loss was a huge blow to the union and gave the confederate army a boost in morale after failed invasion attempt the prior year.
