President Lincoln was thinking of taking a risky step to seal victory. At this point in time he came to the realization that he needed to move in a different direction. The strategic goal to restore the Union was not a good enough reason to keep the Northern states interested and behind the war. Lincoln decided to offer the North a new reason to stay in the fight and the British to stay out of the war, however he needed a good victory under his belt to use for this change in strategic planning. The problem was how to break the news of this change in strategy before the Confederates tore through the union on the battlefield and effected his troops morale.
A month prior Generals Lee and Jackson were crossing guns with Pope at Manassas#. Lee moved his army across the Potomac River into Maryland on September 4, 1862. At this point in time his objective was to claim Harrisburg.# On his way he spread his troops around Maryland to show everyone his strength, gathering supplies#, rounding up volunteers and he also managed to threaten Baltimore, Washington and even Philadelphia. Lee's plan was that McClellan would eventually come out of Washington to fight him and he would have plenty of time to choose the ground that he wanted to fight on and secure the southern victory.
Lee choose the Shenandoah Valley as his supply route. Unfortunately the Union controlled Harpers ferry at the northern opening of the valley. This Union force could cut off the confederate supply route of wagon trains loaded with ammunition, which could