“But suppose in the spring of 1864 [Lincoln] had to muster out of service one of its two primary commands, the Army of the Potomac or Sherman’s Army of the West. How would that have effected the outcome of the war? Could Grant have even adopted this strategy without those 100,000 men? How would the campaign of 1864-65 transpired? Such conjecture helps to elucidate, in just one area, the critical contributions of blacks to the defeat of the Confederacy. During those key months in the late spring and summer, when the picture for the Lincoln administration looked bleakest and the Union desperately struggled to maintain its uniformed strength, more than 100,000 blacks were serving in the Union army and thousands more were in the Federal navy. In fact, there were more blacks in Union blue than either Grant commanded outside Petersburg or Sherman directed around Atlanta. Their absence would have foiled Grant’s strategy and quite possibly doomed efforts at reunion; their presence enabled Grant to embark on a course that promised the greatest hope of Federal victory. At the outbreak of the war, leadership on neither side envisioned the varied and dramatic contributions that blacks would make to Confederate defeat. Nearly 180,000 served in the Union uniform with muskets in hand. As newfound laborers for the Federal war effort, blacks grew cotton and foodstuffs and aided in all sorts of construction and logistical endeavors, and as lost laborers for a fledgling wartime nation that so depended on its slaves for food production and other essentials, blacks caused shortages, hardships and disillusionment among soldiers and civilians alike. Slaves who could not run away to northern lines supported the Union war effort through work sabotage, general unruliness that created insecurity among white southerners, and assistance to Federal troops who escaped from Confederate prison camps. Blacks alone did not win the war, but timely and extensive support from them contributed significantly and may have made the difference between a Union victory and stalemate or defeat.”
— Why the Confederacy Lost, 1992