General William Tecumseh Sherman's March t the Sea in November and December of 1864 marked not only a turning point in the Civil War, but also in military history, and the history of the United States.
Sherman fought differently than the generals of his time, as he believed that to win a war, one must also make war on civilians, who he referred to as "the backers up of things". Destroy everything that might be of use to the enemy, including food, supplies, railroads, etc. This was very hard on the civilian population of Georgia, as it would take them a very long time to recover economically and otherwise. "Total War", therefore, was a new concept, and significant in history.
The savagery of the campaign and the damage his army inflicted also was the final nail in the South's coffin. They were already going to lose, and what Sherman did was speed up the end date of that war, and the depth to which that loss was felt by southerners.
As testament to his efficacy, my Grandmother, a Georgian born well after the Civil War, still cursed Sherman when I was young.