Robert E. Lee's march to Gettysburg in late June 1863 represented the Confederate Army of Northern Virginia's second invasion of Union territory, aimed at shifting the war away from war-torn Virginia and potentially forcing a negotiated peace. Following his victory at Chancellorsville in May, Lee convinced President Jefferson Davis to approve an offensive campaign into Pennsylvania. The army moved north through the Shenandoah Valley in three corps under James Longstreet, Richard Ewell, and A.P. Hill, with Lee initially planning to concentrate his forces near Harrisburg or Philadelphia. However, when Confederate cavalry under J.E.B. Stuart became separated from the main army on a raid around Union forces, Lee lost crucial intelligence about enemy positions. The two armies unexpectedly collided at the small Pennsylvania town of Gettysburg on July 1, 1863, beginning what would become the war's most decisive battle.