The Union had all of the material advantages, the most important of which were their larger population and their far superior economy. Specifically, twenty one million people resided in the North while only nine million resided in the South, four million of which were slaves . The Confederacy had great trouble throughout the war providing their soldiers with essential articles such as shoes, blankets and woolen cloths . The scarcity of resources was greatest in the one or two states nearest its largest armies and "under the wasting consumption of war, " the production of raw material was diminished further. The Confederacy's war tactics were also debilitated by the soldiers" lack of food, a difficulty in supplying their horses, and the impossibility of replacing them. However, the South dominated the beginning stages of the war primarily because of its far superior military leadership. The Confederacy knew this, and that lifted the spirits of the soldiers, and conversely hurt the spirits of the Union soldiers. .
The advantages of both sides proved to be crucial in the two years leading to Gettysburg. While General Robert E. Lee, commander of the army of Northern Virginia, won all of the critical battles, he knew he could not continue fighting this way. As soon as he crushed a company of Union soldiers, the North used its population advantage to immediately send fresh reinforcements. Lee, an avid reader of the Union newspapers, knew that Lincoln had been facing tremendous pressure from some powerful people in the war-weary North to allow the South to secede. For example, proposed peace resolutions put before the New Jersey legislature caused a protest among war volunteers as they stated "traitors at home shall quake with fear ". Lee's intention was to win a critical battle on northern soil, which would not win the war militarily, but would, he believed, bring overwhelming political pressure on Lincoln.