>>512993898
>The federal census of 1860 counted about one hundred thousand free black men and well over eight hundred thousand slaves who would be of military age by 1863—potentially a formidable addition to the Union’s manpower pool.
>The new year was likely to bring further advances by
Union armies and freedom to many more Southern slaves, opening up fertile fields
for recruiters.
"Roughly one-third were Northern born free men"...
https://www.nps.gov/apco/learn/historyculture/united-states-colored-troops-at-appomattox.htm