The Overland Campaign was a thrust necessary for the Union to win the war, and although Grant suffered a number of setbacks, the campaign turned into a strategic success for the Union. By engaging Lee's forces and not permitting them to escape, Grant forced Lee into an untenable position. But this came at a high cost. The campaign was the bloodiest in American history: approximately 55,000 casualties on the Union side (of which 7,600 were killed), 33,600 (4,300 killed) on the Confederate. Lee's losses, although lower in absolute numbers, were higher in percentage (over 50%) than Grant's (about 45%), and more critically, while Grant could expect reinforcements to replace his army's losses, Lee largely could not. His losses were irreplaceable. Furthermore, the public interprets the results of the campaign based on these casualty lists. Dr. Earl Hess states, "The observer should not be fooled by the gory assaults that riveted everyone's attention from Spotsylvania onward—the Overland Campaign was at its heart a campaign of maneuver...Grant's most significant achievement in the Overland Campaign was not capturing territory or reducing the fighting of strength of the Army of Northern Virginia by 50%; rather, it lay in robbing Lee of the opportunity to launch large scale offensives against the Army of the Potomac."