First published in 1944, the Beard's New Basic History of the United States contained the following passage:
In the Proclamation of Emancipation, issued under his war powers, Lincoln declared thenceforward and forever free all the slaves in all the districts of the United States then in arms against the Union. From one point of view this was an empty threat. It freed no slaves in fact. In the loyal districts of the Union slaves remained slaves and, in the districts still controlled by Confederate arms, slaves also remained slaves. But the Proclamation electrified the imagination of all who loved liberty and was indeed a move toward the abolition of slavery throughout the United States.
For Jefferson Davis, as well as Abraham Lincoln, emancipation became a practical issue before the close of the conflict. In desperate straits for soldiers to fight its battles, the Confederate Congress, near the end of the war, passed an act for the employment of slaves in military services. That law had the approval of General Robert E. Lee, as well as of President Davis, and he aided in recruiting Negroes as soldiers. While the language of the statute and of the orders issued under it was vague, it was interpreted to mean that a slave acquired freedom by joining the Confederate army.
Even plans for complete emancipation were discussed at the Confederate capital. In 1864, Duncan Kenner, a member of the Confederate Congress, proposed to President Davis that an agent be sent abroad with power to offer to the British and French governments the emancipation of slaves in exchange for their official recognition of the Confederacy. Davis acceded to the plan. He appointed Kenner as minister plenipotentiary to carry out the project; and Kenner was abroad working at the scheme early in 1865—too late. Had the war continued, real emancipation might have been a Southern act of war. (Bold-faced text added)
Interestingly, Confederate general, John B. Gordon, addressed the issue in his work, Reminiscences of the Civil War, which adds some interesting details and anecdotes to the concept of slave enlistments in Confederate army.
. . . it was no longer possible to fill our ranks except by converting slaves into soldiers: while the great Government at Washington could enlist men not only from the populous States of the Union, but from the teeming populations of foreign countries.
It was during this doleful period that the suggestion to give freedom to Southern Slaves and arm them for Southern defence became the pressing, vital problem at Richmond. It had been seriously considered for a long period by the civil authorities, and the opinions of certain officers in the field were at this time formally solicited. General Lee strongly favored it, and so did many members of Congress; but the bill as finally passed was absurdly deficient in the most important provisions. It did not make plain the fact that the slave’s enlistment would at once secure his freedom. Public sentiment was widely divided as to the policy of such a step. In its favor was the stern fact, universally recognized, that it was no longer possible to fill our ranks except by converting slaves into soldiers: while the great Government at Washington could enlist men not only from the populous States of the Union, but from the teeming populations of foreign countries. Again, it was argued in favor of the proposition that the loyalty and proven devotion of the Southern negroes to their owners would make them serviceable and reliable as fighters, while their inherited habits of obedience would make it easy to drill and discipline them. The fidelity of the race during the past years of the war, their refusal to strike for their freedom in any organized movement that would involve the peace and safety of the communities where they largely outnumbered the whites, and the innumerable instances of individual devotion to masters and their families, which have never been equaled in any servile race, were all considered as arguments for the enlistment of slaves as Confederate soldiers. Indeed, many of them who were with the army as body-servants repeatedly risked their lives in following their young masters and bringing them off the battlefield when wounded or dead. These faithful servants at that time boasted of being Confederates, and many of them meet now with the veterans in their reunions, and, pointing to their Confederate badges, relate with great satisfaction and pride their experiences and services during the war. One of them, who attends nearly all the reunions, can, after a lapse of nearly forty years, repeat from memory the roll-call of the company to which his master belonged. General Lee used to tell with decided relish of the old negro (a cook of one of his officers) who called to see him at his headquarters. He was shown into the general’s presence, and, pulling off his hat, he said, “General Lee, I been wanting to see you a long time. I’m a soldier.”
“Ah? To what army do you belong—to the Union army or the Southern army?”
“Oh, general, I belong to your army.”
“Well, have you been shot?”
“No, sir; I ain’t been shot yet.”
“How is that? Nearly all of our men get shot.”
“Why, general, I ain’t been shot ‘cause I stays back whar de generals stay.”
Against the enlistment of negroes were urged the facts that they were needed—were absolutely essential—on the plantations to produce supplies for the armies and the people; that even with their labor the country was exhausted, and without it neither armies nor the people at home could survive; that the sentiment of the army itself was not prepared for it, and that our condition was too critical for radical experiments.