The campaign started with a tactical defeat at Kernstown on March 23, 1862, when faulty intelligence led him to believe he was attacking a small detachment. But it became a strategic victory for the Confederacy, because his aggressiveness suggested that he possessed a much larger force, convincing President Abraham Lincoln to keep Banks' troops in the Valley and McDowell's 30,000-man corps near Fredericksburg, subtracting about 50,000 soldiers from McClellan's invasion force. As it transpired, it was Jackson's only defeat in the Valley.