Large numbers of rebel troops captured at Vicksburg in violation of their paroles were re-captured at Chattanooga. This was big reason the exchange cartels broke down. The rebels would not abide by them.
The rebel government allowed Union prisoners to languish in hell holes. It may be that this was the intentional or de facto policy of the rebel government in order to pressure the federals into a return to the exchange cartels. They wanted this because their available manpower was less than the north's.
The federals, in an attempt to force better treatment for Union prisoners, made a policy of keeping rebel prisoners in conditions similar to those known to be inflicted on Union prisoners.
The rebels took the lead in all this, as they did in all atrocity and horror in the war.
Walt