Major General Joseph Hooker commanded the Union Army of Potomac. There were over ninety thousand men in his army. Later, President Abraham Lincoln would replace Hooker with Major General George G. Meade, since Hooker had proved to be a failure during the previous battles.6
In the middle of June, the Confederate Army crossed the Potomac River and entered Maryland and southern Pennsylvania.7 Hooker's Union Army followed, staying between Washington D.C. and the Confederates, so that in order for Lee's army to attack the capital, they would have to get through the Union Army first. Trying to avoid the Union army, General Lee allowed J.E.B. Stuart to take some of the troops and go around the Union army. Meanwhile, in a controversial move, Lee allowed J.E.B. Stuart to take a portion of the army's cavalry and ride around the Union army. The plan did not work, however, because Lee had not given clear orders, and Stuart was an incompetent officer. Therefore, Stuart and Lee's three best brigades were not present in the army