After his success at Chancellorsville, Lee led his army through the Shenandoah Valley to begin his second invasion of the North. With his army in high spirits, he intended to move the focus of the summer campaign from war-ravaged northern Virginia and hoped to influence Northern politicians to give up their prosecution of the war by penetrating as far as Harrisburg, Pennsylvania, or even Philadelphia. The opposing armies began to collide at Gettysburg on July 1, 1863, as Lee urgently concentrated his forces there, his objective to engage the Union army and destroy it. Low ridges to the northwest of town were defended initially by a Union cavalry division, which was soon reinforced with two corps of Union infantry. This began a 3-day battle which many consider determined the fate of the War in the Eastern theatre.