With Pope's retreat, Lee takes the offensive, but in one of those small moments that alter history, a copy of his roders fall into Union hands, allowing McClellan to anticipate Lee's strategy. In this single bloodiest day of the war, McClellan's Union forces meet Lee's advancing army. The dead and wounded exceed 10,000 for both sides. Lee pulls back, his invasion blunted, but McClellan fails to pursue the retreating Confederates. With Lee's offensive stalled, the likelihood of European recognition of the Confederacy is sharply reduced.