There were over 400,000 prisoners of the Civil War. Towards the beginning of the war, privates, sergeants, and captains were being traded on the battle field. In July 1862, Major General John A. Dix of Union Army conferenced with the Confederate representative, Major General Daniel H. Hill, in regards of the prisoner exchange. A draft providing parole for the trades began to break out, and was later approved, signed, and ratified. It became known as the Dix-Hill Cartel.
Unfortunately, the Dix-Hill Cartel failed not long after due to the Confederate Government refusing to parole black prisoners, and threatened to treat them as slaves. Vicksburg was one who had given up on July 4, and at that time, most Confederate prisoners who had been paroled were back in the trenches.