The American Civil War presented an exceptional state of affairs in modern warfare, because strong personalities could embed their own command philosophies into field armies, due to the miniscule size of the prior US military establishment. The effectiveness of the Union Army of the Tennessee stemmed in large part from the strong influence of Ulysses S. Grant, who as early as the fall of 1861 imbued in the organization an aggressive mind-set. However, Grant’s command culture went beyond simple aggressiveness – it included an emphasis on suppressing internal rivalries among sometimes prideful officers for the sake of winning victories. In the winter of 1861 and the spring of 1862, the Army of the Tennessee was organized and consolidated into a single force, and, despite deficits in trained personnel as compared to other Union field armies, Grant established important precedents for both his soldiers and officers that would resonate even after his departure to the east. The capture of Vicksburg the following summer represented the culminating triumph of that army, cementing the self-confident force that would later capture Atlanta and win the war in the western theater.

When Gen. Robert E. Lee assumed command of the Army of Northern Virginia on June 1, 1862, it was essentially an amalgamation of units, not a united force. Lee gave the army a distinctive organizational culture based on his belief that if the Confederacy were to win the war, it would have to do so quickly. This necessitated an operational strategy that emphasized seizing the initiative, even though his army always faced a numerically superior foe. Implementation of this strategy required aggressive leadership at all levels, particularly among Lee’s top subordinates. Lee secured this kind of leadership by systematically ridding himself of senior lieutenants who proved cautious in battle while forgiving mistakes, even expensive ones, on the part of subordinates who showed themselves to be offensive-minded. This “embedding mechanism,” as specialists in management science would call it, sent an unmistakable signal to the rest of the army’s leaders that they were expected to be bold in action. Lee’s aggressive strategy sought to destroy the enemy army, but his ultimate goal was to demoralize Northern public opinion, which he regarded as the Union’s center of gravity. Although he failed to accomplish this, Lee's many battlefield victories made his army the focus of Confederate nationalism, so that his surrender at Appomattox equated with the death of the Confederacy.