Bigelow opened his chapter on the subject by excerpting from Ulysses Grant's memoirs, specifically recalling the Union commander's comments on Sherman's march through the South:
It had an important bearing in various ways upon the great object we had in view, that of closing the war. All the States east of the Mississippi River, up to the State of Georgia, had felt the hardships of the war. Georgia and South Carolina, and almost all of North Carolina, up to this time had been exempt from invasion by the Northern armies, except upon their immediate sea-coasts. Their newspapers had given such an account of Confederate success that the people who remained at home had been convinced that the Yankees had been whipped from first to last, and driven from pillar to post, and that now they could hardly be holding out for any other purpose than to find a way out of the war with honor to themselves.
Even during this march of Sherman's, the newspapers in his front were proclaiming daily that his army was nothing better than a mob of men who were frightened out of their wits, and hastening, panic-stricken, to try to get under cover of our navy for protection against the Southern people. As this army was seen marching on triumphantly, however, the minds of the people became disabused, and they saw the true state of affairs. In turn they became disheartened, and would have been glad to submit without compromise. (p. 225)The old anarchist and Marxist idea of the "propaganda of the deed" has enjoyed something of a resurgence lately in terrorism and insurgency studies. In its original conception, propagande par le fait was about the catalyzing political effect of public violence: through bomb blasts or political killings, individuals could provoke a demonstration of the government's brutality and impotence against committed revolutionaries, inspiring widespread resistance by the masses.
But there's a flip side to that idea, too: if the counter-revolutionary can synthesize his actions with his political message to counter or even pre-empt the challenging narrative, he can demonstrate the bankruptcy of the rebel's self-annihilating concept. This approach can be extended beyond counterinsurgency and irregular warfare and into the "political strategy" that Bigelow juxtaposes with the "regular [military] strategy" of Jomini: by marching through Georgia and making war on the Confederate populace, Sherman obliterated the fantasy narrative that sustained the last vestiges of popular support for the Southern cause. It wasn't enough for Grant's army to inflict staggering losses on Confederate forces -- without fighting a single battle, Sherman made certain the people of the rebellious states bore personal witness to the irrepressible Union army and understood the fraud their own leaders continued to perpetrate on them.
In other words (to put it in a popular modern context): "you want it to be one way, but it's the other way."
Don't forget, this was an era when battle was widely thought to be singularly decisive (even by Grant himself, who began the war with very different ideas about the utility of maneuver vis-a-vis attritive engagements with the main enemy force). And yet the "IO impact" (to use a modern term) of Sherman's operations was indisputable, and perhaps in some ways conclusive.