His past and present are mixed. The past is the savage, brother-kill-brother world of the Civil War. It's the storming of Missionary Ridge and a new command, a command comprised entirely of liberated slaves. And there's a prisoner from the notorious Quantrill's Raiders who escapes from Captain Josiah Hedges and later meets him again.
Used availability for George G Gilman's Vengeance Is Black
November 1989 : USA Mass Market Paperback
November 1973 : UK Paperback
November 2012 : USA, Canada, UK Kindle edition