The bad conditions inside the graveyard contributed to a city-wide epidemic after the battle. Prisoner exchanges The extensive period of conflict during the American Revolutionary War and Napoleonic Wars (1793–1815), followed by the Anglo-American War of 1812, led to the emergence of a cartel system for the exchange of prisoners, even while the belligerents were at war. A cartel was usually arranged by the respective armed service for the exchange of like-ranked personnel. The aim was to achieve a reduction in the number of prisoners held, while at the same time alleviating shortages of skilled personnel in the home country. American Civil War At the start of the American Civil War a system of paroles operated. Captives agreed not to fight until they were officially exchanged. Meanwhile, they were held in camps run by their own army where they were paid but not allowed to perform any military duties. The system of exchanges collapsed in 1863 when the Confederacy refused to exchange black prisoners. In the late summer of 1864, a year after the Dix–Hill Cartel was suspended, Confederate officials approached Union General Benjamin Butler, Union Commissioner of Exchange, about resuming the cartel and including the black prisoners. Butler contacted Grant for guidance on the issue, and Grant responded to Butler on 18 August 1864 with his now famous statement. He rejected the offer, stating in essence, that the Union could afford to leave their men in captivity, the Confederacy could not. After that about 56,000 of the 409,000 POWs died in prisons during the American Civil War, accounting for nearly 10% of the conflict's fatalities. Of the 45,000 Union prisoners of war confined in Camp Sumter, located near Andersonville, Georgia, 13,000 (28%) died. At Camp Douglas in Chicago, Illinois, 10% of its Confederate prisoners died during one cold winter month; and Elmira Prison in New York state, with a death rate of 25% (2,963), nearly equalled that of Andersonville. Amelioration During the 19th century, there were increased efforts to improve the treatment and processing of prisoners. As a result of these emerging conventions, a number of international conferences were held, starting with the Brussels Conference of 1874, with nations agreeing that it was necessary to prevent inhumane treatment of prisoners and the use of weapons causing unnecessary harm. Although no agreements were immediately ratified by the participating nations, work was continued that resulted in new conventions being adopted and