Funny claim, that. Made, obviously, to prove that slaves were really quite happy with their lot in the South, and when that way of life was threatened by the "Northern War of Aggression," they willingly picked up arms to defend Massa and the Missus against the Yankees.
I just finished reading a history of the Civil War ("The American Civil War: A Military History," by John Keegan: Alfred A. Knopf, 2009) and remembered that Keegan had some things to say about the participation of ex-slaves in the armies of the North ... and this bit following about certain proposals by some Southerners to force slaves into defending the South:
At the very end of the war, as the clouds of defeat began to gather over the Confederacy, there arose a mood even there to make good its growing shortage of manpower by enlisting slaves. The proposal to arm and train slaves as soldiers, advanced by General Patrick Cleburne of the Army of Tennessee in January 1864, found favour with many of his senior subordinates, who accepted his argument that black enlistments would greatly expand the South's fighting strength. Others, however, violently disagreed. Cleburne's proposal simply caused division and ill feeling until Jefferson Davis [president of the Confederacy] forbade its being further discussed or even mentioned. By November 1864, however, Davis called on the Confederate Congress for permission to purchase slaves to be used as military cooks and transport drivers .... [The Confederate] Congress, however, drew back ..., with the former presidential candidate Howell Cobb stating, "You cannot make soldiers of slaves or slaves of soldiers. The day you make soldiers of them is the beginning of the end of the revolution. If slaves will make good soldiers our whole theory of slavery is wrong."
Take time to think about how enlisting slaves to save the institution of slavery would expose the practice to ridicule. Cobb was right. Plus the Nat Turner slave rebellion in Virginia, which preceded the Civil War by a couple of decades, could still sent a shiver of fear down the backs of many Southerners who contemplated for even a second the thought of hundreds of slaves holding guns and bayonets.
General Robert E. Lee weighed in on the issue in February 1865, just a couple of months before his forced surrender to U.S. Grant. Lee wrote a letter to a Confederate congressman in which he concluded that "if the enlistment of blacks was the only means to avert defeat, then blacks must be accepted as soldiers."
By March 1865, the Confederate Congress officially called on slave owners to make up to a quarter of the slaves in any one state available for military service. Eventually only two companies of black soldiers were enrolled, and they had taken no part in fighting before the Union army arrived in Richmond to impose surrender.
In other words, though moves were afoot to try to enlist slave soldiers to save the Confederacy during its death throes, only about 200 were ever mustered in, and those never took part in any battle.
So much for the bogus claim that African Americans fought "in large numbers" for the South.
Southern generals were justifiably worried about what sort of fighters coerced slaves would be. Black soldiers fought very well for the Union, incidentally, but they were literally and figuratively fighting for their individual freedoms. Ultimately, between 180,000 and 200,000 black men served in the Northern armies. Twenty-three of those soldiers won the Congressional Medal of Honor before Appomattox.