In July 1862, after a series of Union military setbacks, President Abraham Lincoln wrote that slavery was the “the heart of the rebellion.” Lincoln recognized how slavery provided the South with cheap labor that could sustain Southern agriculture and industry while the white population went to war. Slaves also provided valuable military service, constructing fortresses and infrastructure that enhanced Confederate combat power and mobility. Destroying slavery, Lincoln understood, could deny the South a valuable source of productive strength that would reduce the Confederacy’s military and economic power.
Over the next three years, Union military strategy evolved from its initial conciliatory phase to the “hard hand” phase that sought to destroy Southern military power—a power that owed much to the institution of slavery. The most famous campaign of the “hard hand” phase of the war was General William T. Sherman’s 1864-1865 campaign in Georgia and the Carolinas—the birthplace of the insurrection. The campaign, which started with the burning of Atlanta and ended with a furious, vengeful march through the Carolinas, brought the Union Army into some of the South’s largest slave plantations. The presence of Sherman’s armies inspired countless blacks to flee slavery into Union lines. This influx of blacks into Sherman’s ranks enhanced Union intelligence and combat power, while dealing a devastating blow to the South’s ability and will to fight. Sherman’s campaign, therefore, helped plant a knife through the heart of the rebellion.
When Sherman entered Georgia in mid-1864, his three armies inspired and enabled countless slaves to escape from bondage into the Union lines. Thousands of these escaped slaves crowed into the rear of Sherman’s advancing armies. So long as they remained within Union lines, where they could evade recapture, they were free—a freedom legally guaranteed by President Abraham Lincoln’s 1863 Emancipation Proclamation that declared all blacks living in states that remained in open rebellion “then thenceforward forever free.” Entering Union lines offered more than protection and freedom – it also offered promises of economic gain. In January 1865, General Sherman, in the aftermath of his famous march to the sea from Atlanta, issued Special Field Order 15. This order set aside large swaths of fertile, coastal land that stretched from north Florida to South Carolina “for the settlement of the negroes now made free.” Around 20,000 blacks settled this land by the end of the war. In return for promises of freedom, economic gain, and an opportunity to undermine the society that had placed them in bondage, slaves provided vital support to the Union Army that helped quell the Southern insurrection.
Escaped slaves provided Sherman’s Army with critical intelligence on the physical and political landscape of its area of operations. Moving armies over long distances in an era when maps and roads were highly unreliable was a significant challenge to military commanders. However, Sherman’s campaign benefited from the influx of escaped slaves, many of whom had lived and worked their entire lives in the fields and towns of Georgia and the Carolinas. These escaped slaves likely provided critical intelligence on the locations of river crossings, impassable terrain, water sources, etc. In addition to providing support with navigation, escaped slaves probably had some awareness of who were rebel sympathizers. These sympathizers, throughout the war, aided or participated in guerilla raids that harassed Union lines and drained valuable resources from the front. Information on who supported these raids would have helped Sherman’s armies implement more effective counterinsurgency operations. It would also have allowed the Union forces to focus the intensity of their “hard war” policies on the rebellion’s strongest sympathizers, while sparing loyal Unionists. Without the aid of escaped slaves, who served as important intelligence assets, the Union Army’s march across Georgia and into the Carolinas would likely have moved much slower and may have encountered more guerilla resistance.
While ex-slaves helped navigate the Union Armies across hostile, unpredictable terrain, other ex-slaves provided valuable combat support services that enhanced the mobility and combat power of Sherman’s Armies. Although Sherman himself was not a proponent of emancipation, he recognized the value blacks could provide his army in combat support. Union Armies, by late 1864, occupied over 100,000 square miles of enemy territory—territory that drained critical manpower and resources to hold and tame. Taming the land often required large garrisons of troops, reducing the amount of combat forces at the disposal of commanders in battle. Escaped slaves offered Sherman and other commanders a solution to this problem. Instead of using professional soldiers to garrison forts and protect their lengthy, vulnerable lines of communication, Union commanders utilized escaped slaves and, later in the war, black soldiers who were increasingly coming into their lines as the war progressed. While on the march, Sherman’s armies used the ex-slaves to drive wagons, herd livestock, chop wood, and construct and repair transportation networks. With an increased supply of labor, provided by escaped slaves, Sherman’s Armies were able to better supply their armies and concentrate more combat power in battle, rather than diffusing it to protect the ever-expanding Union lines of communication.
Each slave removed from bondage decreased the power of the Confederate Army. Slaves were critical resources for the South; they helped maintain its ability to wage war and sustain its economy. Slaves worked the fields, produced ammunition, and built fortifications, enabling white, male Southerners to fill the army’s ranks. But, by 1864, slaves were becoming scarcer resources; Georgia alone had lost over 60,000 slaves. Without this pool of cheap labor, whites would have had to fill these important economic and military support roles, reducing the manpower allotted to the front line. Southern farmers, by late 1864, worried they would be unable maintain their agricultural output, leading to political pressure on the Confederate government.
General Sherman, as early as August 1862, had recognized the importance of removing slaves from the South to deny them a source of economic and military labor. By 1863, General Halleck, General in Chief of the Union Army, agreed with Sherman’s assessment and made it official Army policy “to withdraw from the enemy as much productive labor as possible.” Halleck argued, “[s]o long as the rebels retain and employ their slaves in producing grains, they can employ all the whites in the field. Every slave withdrawn from the enemy, is equivalent to a white man put hors de combat.” Even regular Union soldiers and officers had recognized the importance of slaves to the South’s capability to wage war. In response to the Second Confiscation Act of 1862, a colonel of the 5th Minnesota observed how confiscating slaves was “striking a blow at the heart of the rebellion.”
The South also recognized the importance of slavery to its military and economic power. In February 1863, Governor John Milton of Florida argued, “Upon slave labor, the Agriculture of Southern States is mainly dependent.” Milton added that slave labor secures “subsistence for the armies in the field, the support of families at home, and…ensure[s] the revenue necessary to the Confederate and State Governments.” The importance of slavery to the South was evident by large-scale movements of slaves away from approaching Union armies, which, slaveholders feared, would free their slaves. In 1864, Congressman Warren Aiken of Georgia, observing the importance of slaves in Southern society, commented on how slaveholders would “give up their sons, husbands, brothers & friends…to the army; but let one of their negroes be taken, and what a houl you will hear.” Sherman’s march through Georgia and the Carolinas certainly made Southern slaveholders howl, as it pulled in escaped slaves and used their knowledge and skills against their former masters.
In addition to the material consequences of Sherman’s campaign in Georgia and the Carolinas, the campaign dealt a serious psychological blow to the South that reduced its will to wage war. The psychological shock produced by the freeing slaves in Georgia and the Carolinas sparked deep fears among local residents. Georgians, like Congressman Warren Aiken of Georgia, worried how free slaves will lead to white subjugation. “We and our children,” Aiken feared, “will be slaves, while our freed negroes will lord it over us.” Whites also feared how freed blacks may instigate a race war. This fear spread throughout Southern society and into the ranks of the Confederate Army, where soldiers began to worry about the welfare of the family and farms, leading many to desert and return home.
With Southern morale collapsing in the face of Sherman’s onslaught through Georgia and the Carolinas, the fabric of the slave system unraveled. Slave flight shed light on the inhumanity of the system, as countless blacks risked their lives to escape and head towards battle, rather than continue to live in bondage. Some even chose to take their own lives when caught to avoid the horrors of slavery. Despite the dangers, slaves continued to escape, demonstrating the declining power and influence of the slaveholder. As the institution of slavery declined, white Southerners even began to consider employing blacks in their own military with a promise of freedom. One Georgian wrote to President Jefferson Davis after Sherman conquered Atlanta and pleaded for the South to conscript blacks and “force them into the army… upon the condition, if necessary, of freedom after the war.” The Confederate government eventually agreed to black conscription in March 1865, but, by then, it was too late; Lee’s Army surrendered at Appomattox a mother later. The war was over. Slavery officially died less than a year later with the passing of the Thirteenth Amendment that officially outlawed the institution that had become the heart of Southern power.
General Sherman’s campaign in Georgia and the Carolinas dealt a devastating physical blow to the South’s ability to wage war, by destroying and confiscating irreplaceable resources and draining the heartland of the Confederacy of its critical slave labor, which, simultaneously, enhancing the intelligence and combat power of Union forces. This physical shock also produced a potent psychological shock to the South by exposing the frailty and corruptness of its social order. Combined, the physical and psychological shock produced by Sherman’s advancing armies helped destroy the ability and the will of the South to continue its insurrection.
 James M. McPherson, “Tried by War: Lincoln as Self-Taught Strategist,” Major Problems in the Civil War and Reconstruction, ed. Michael Perman, 2nd ed. (Boston: Wadsworth, 1998), 183.
 Mark Grimsley, Hard Hand of War: Union Military Policy Toward Southern Civilians 1861-1865 (New York: Cambridge University Press, 1995), 122.
 Ibid., 2.
 Ira Berlin and others, Slaves No More: Three Essays on Emancipation and the Civil War (Cambridge: Cambridge University Press, 1992), 68.
Ira Berlin and others, eds., Free at Last: A Documentary History of Slavery, Freedom, and the Civil War, ed. Ira Berlin and others (New York: New Press, 1992), 71.
 Ibid., 318.
 Ira Berlin and others, Slaves No More, 176.
 Ira Berlin and others, Slaves No More, 31.
 General William T. Sherman to Thomas Hunton, August 24, 1862, in Free at Last, ed. Berlin and others (New York: New Press, 1992), 68.
 Grimsley, The Hard Hand of War, 165.
 Berlin and others, eds., Free at Last, 436.
 Berlin and others, Slaves No More, 129.
 Robert Q. Mallard and others to Brigadier General Hugh M. Mercer, August 1, 1862, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 61.
 Ira Berlin and others, eds., Free at Last, 129.
 Wm D. Taylor and others to President Jefferson Davis, October 13, 1864, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 153-154.
 General William T. Sherman to Thomas Hunton, August 24, 1862, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 70.
 General in Chief Henry W. Halleck to Major General Ulysses S. Grant, March 31, 1863, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 101.
 James M. McPherson, For Cause and Comrades: Why Men Fought in the Civil War (New York: Oxford University Press, 1997), 120.
 Governor John Milton to Hon. James A. Seddon, February 17, 1863, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 130.
 Ibid., 131.
 O.G. Eiland to President Jefferson Davis, July 30, 1863, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 133.
Warren Aiken to Nathan Land, October 13, 1864, in Major Problems in the Civil War and Reconstruction, ed. Perman, 2nd ed. (Boston: Wadsworth, 1998), 223.
 Pierre Soniat to General Nathaniel P. Banks, December 20, 1862, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992),, 84.
 Grimsley, The Hard Hand of War, 170.
 Pleas. Smith to A.A.G.J. Thompson, January 8, 1863, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 96.
F. Kendall to President Jefferson Davis, September 16, 1864, in Free at Last, ed. Ira Berlin and others (New York: New Press, 1992), 151.