Hello all, with respect to the issue of Prisoner exchanges between the U.S. and the C.S.A There was indeed such a program, but it was stopped. I wrote this for another site, and will paste it here for whatever light it may shed on this thread.
"I had read that it was Lincoln, and Grant that stopped the exchanges due to Confederate refusal to treat all Union soldiers equally, (some mention of a massacre of Black soldiers was made.) I found this info which makes no mention of said mistreatment, but lays the blame on a few specific people.
In 1862 Representatives of each side met to arrange the format of exchanges, and how many of a particular rank were equal in value to higher officers etc.
Gen. John Dix (U.S.) and Gen. D.H. Hill (CSA) were these representatives.
In 1863 Gen. Henry Halleck (U.S.) became the representative in authority for the exchanges. He was pressured by Edwin Stanton then Secretary of War for the U.S. who proceeded to impede the program, and when Gen U.S. Grant was made the overall Commander of the Army the exchanges trickled away to nothing.(cut & paste follows)
General Benjamin F. Butler later said what Grant had told him: "He (Grant) said that I would agree with him that by the exchange of prisoners we get no men fit to go into our army, and every soldier we gave the Confederates went immediately into theirs, so that the exchange was virtually so much aid to them and none to us."
This would account for the huge numbers of prisoners needing to be held in spaces never designed for such great numbers. Camp Sumter (Andersonville Prison) was designed for no more than 10,000, but eventually held as many as 30,000. I have visited Andersonville, and the thought of 30K people being interned in this small space is appalling.