In the spring of 1864, Ulysses S. Grant had adopted a new strategy in dealing with Robert E. Lee's Army of Northern Virginia. Recognizing that Lee's army was bound to protect Richmond, and that his own army had a numerical advantage, Grant ordered a series of attempts to outflank Lee's army on its right. As the Confederates moved to check this maneuver, they armies collided at the Wilderness (May 5-7) and at Spotsylvania Court House (May 8-20). The result was some of the most savage and bloody fighting of the war, with the Union army unsuccessful in outflanking their opponents. But Grant continued to move south on the right flank, and on June 3 he ordered an ill-advised assault on entrenched Confederate positions at Cold Harbor. The result was a nightmare for the Union Army. The Confederates, secure in their position, mowed down successive waves of Union soldiers, and the Federals suffered 7,000 casualties before abandoning the assault. Grant later declared the decision at Cold Harbor as his worst mistake of the war. He later wrote in his memoirs, "I have always regretted that the last assault at Cold Harbor was ever made...At Cold Harbor no advantage whatever was gained to compensate for the heavy loss we sustained." Yet rather than retreating after this stunning repulse, as so many of his predecessors had done in Virginia, he continued to press forward on the Confederate right, moving toward Petersburg, where the two armies would dig in for a bloody siege that ultimately shattered the Confederate army.