Although the code was issued as only an order for the United States army, it was eventually adopted by the Confederacy, and other armies across the world. It became one of the foundational expressions of the international laws of war. It said that war was between societies, so that civilians of the opposing nation were indeed enemies, but it also said that they should be spared whenever militarily possible. It also established rules for dealing with captured property, both public and private, spies, deserters. You can read the entire order here.