There is little question that Sherman operated against American civilians in the South with the full approval of Lincoln and Grant, who must also share the responsibility for visiting total war upon defenseless men, women and children. This executive approval of war against civilians was not lost on the young Spanish attache to the Northern army, Valeriano Weyler, who became known in mid-1890s Cuba as General “Butcher” Weyler. To discourage Cuban freedom fighters, Weyler herded their women and children into concentration camps after burning their homes.
Bernhard Thuersam, www.Circa1865.com The Great American Political Divide
Sherman’s New Notion of Total War
“Major-General [Henry W.] Halleck, Sherman’s overall commander-in-chief, was an accepted authority of his day on the rules governing the intercourse of nations and the laws of war. Sherman had attended West Point with Halleck, and certainly curiosity if not actual interest on the subject would have prompted him to look into Halleck’s “International Law.”
It was said of Sherman that he was in the habit of “starting new notions constantly in his own brain, and following them up, no matter how far or whither they led.” On October 4  he reported to General Grant that two more steamboats had been fired upon – the attacks being described by Sherman as wanton and cruel – and he informed Grant of the new notion that had occurred to him:
“I caused Randolph [Mississippi] to be destroyed, and have given notice that a repetition will justify measures of retaliation, such as loading boats with their captive guerillas as targets (I always have a lot on hand), and expelling families from the comforts of Memphis, whose husbands and brothers go to make up the guerillas. I will watch Randolph closely, and if anything occurs there again I will send a brigade by land back of Randolph and clean out the country.”
From this modest beginning – the experiments to discover the effectiveness of the practical application of his concepts of total war – the destruction of property, the holding of hostages and now the improper exposure of prisoners to the fire of their own forces, would not be enlarged on in the weeks ahead and their effects carefully noted.
Whether Sherman himself ever entertained any doubts or hesitations as to the course to which he had committed himself cannot be stated accurately, but it is noteworthy that during this period no mention is made in his correspondence of the rules of war, nor does he suggest that his actions were not in accord with them.
There are threads of justification woven into his letters and his orders for extreme severity and barbarism; and a definite impression is left that many of these were included with one eye on posterity and the hope of ultimate vindication.”
(Merchant of Terror: General Sherman and Total War; John Bennett Walters, Bobbs-Merrill Company, 1973, excerpt, pp. 68-69)