The Union's harvest of southern black antiConfederates widened its economic, home front, and especially manpower advantages. By garrisoning captured forts, guarding railroad tracks, and protecting contraband camps, black troops freed white troops to lend Grant's and Sherman's advancing armies overwhelming numerical superiority. Ex-slaves also contributed one-eighth of Grant's eastern armies during their final siege of Lee and much of Sherman's military labor during his climactic march through Georgia and the Carolinas.
Abolitionists had told the pre-1863 Lincoln that an emancipation proclamation would make one equal two. One slave emancipated would yield one worker lost to the Confederacy plus one worker gained for the Union. After January 1, 1863, Lincoln helped to achieve just this result. Something like