Why did Sherman and his army so completely devastate the land barns and houses in Georgia and South Carolina?

Answer 1

Tactically - to allow him to live off the land, and ignore his increasingly vulnerable supply line.

Strategically - to attack the civilian underpinning of the Confederate armies, bri ng them closer to starvation, and signal to the world that the Confederacy was on its last legs.

This clearly shortened the war by months.

Answer 2

Prior to 1864, most of the Civil War battles had occurred in the region surrounding Washington DC, from Pennsylvania to northern Virgina. In 1864, President Abraham Lincoln and General U. S. Grant decided that the time had come to take the war to the "Deep South", both for tactical and for psychological effect. Grant was occupied with General Robert E. Lee's Army, dug in and fortified in northern Virginia. Much of Lee's food and supplies were coming from Georgia, and from the Shenandoah Valley of western Virginia.

So General Philip Sheridan was sent to the Shenandoah Valley to destroy its agricultural use by "scorched earth" tactics. General William Tecumseh Sherman was send to capture and to largely destroy the City of Atlanta and from there he proceded to march across the state to Savannah, applying the "scorched earth" policy by destroying crops, railroads and buildings across the middle of the Confederacy.

Sherman's march not only destroyed a great deal of the Confederacy's ability to supply its troops, but it placed Sherman to the south of Lee's huge army so that Lee now faced a double threat with Grant to the north and Sherman to the south.

Answer 3

He conducted "Total War" demonstrating to the Confederacy that a Union Army could march through the heartland of the Confederacy, in the hopes of bringing the lengthy war to a rapid conclusion