By 1863, there was no longer any doubt that the Civil War had become what Abraham Lincoln had once warned against --"a remorseless revolutionary struggle." The Emancipation Proclamation on January 1 marked a pivotal shift in the conflict. Not only had the Union army begun openly liberating Confederate slaves, but also that army was now officially enlisting black troops. Confederates responded by removing tens of thousands of slaves into the southern interior and by dramatically expanding their military horizons. Robert E. Lee's Army of Northern Virginia invaded Pennsylvania in June. The subsequent Union victory at Gettysburg, coupled with the Confederate surrender at Vicksburg along the Mississippi, has since been identified by many as the war's great turning point, yet the fighting continued without any clear resolution in sight. During that long, hard year, the strain on both societies proved almost unbearable and each side showed serious signs of exhaustion. Yet Union morale rose significantly in the fall with political victories in key states and hard-fought military victories in Tennessee, Thus, when President Lincoln acknowledged the nation's "unfinished work" in his stirring address at Gettysburg in November, it was with solemn, yet hopeful, determination.