After reoccupying Jackson (he had taken the city the first time on May 14, during the Vicksburg campaign), Sherman ordered his men to devastate the area's war-making potential by ripping up railroads, burning enemy supply facilities, and destroying much of the city itself.
In a summon note: THEY WERE ORDERED TO DEVASTE THE CITY.
The part that Sherman didn't like was the stealing, and plundering.