The decision to practice what historians call “total war” on the increasingly defenseless countryside of Virginia and Georgia were personal, practical, tactical and strategic.
From Generals to individual units of soldiers, men made the decision to lay waste at least in part due to hatred of all things southern. These soldiers had been dragged from their homes, marched hundreds of miles, witnessed slaughter after slaughter, lost the bulk of their regiments as they were thrown into the carnage time and again, and many of the them had no idea what the South was really fighting for. They surely believed that whatever it was, it wasn’t possibly worth the blood and sacrifice on either side. So Union soldiers in the Virginia and Georgia theaters of war often became callous and indifferent to suffering, seizing civilian food supplies for their own needs, burning the homes of southern supporters, politicians and military leaders, virtually destroying large swaths of land and property because they could, and they wanted to, and to hell with the Confederacy.
Men like Union General William Tecumseh Sherman were more detached, claiming that “War is all hell, and there is no use trying to reform it”. Sherman was marching to the sea in late 1864, on his own hitch and away from any supply line. He had the approval of Lincoln, and his men needed what the supplies they needed, simple as that. But more so, he viewed "scorched earth" policies as smart strategy to deny anything to the rebels that might help them continue to prosecute the war. He believed that making war on civilians, cruel as it may be in the short term, ended the larger cruelty of the war more quickly. And on another level, Sherman and other commanders believed that making Georgia “howl” (and to an even greater degree, South Carolina after that) would seriously discourage any thoughts of future rebellions. The idea was to make southerners hate war so much that they would be less likely to consider resorting to it again.