The law of war is part of who we are. George Washington, as Commander in Chief of the Continental Army, agreed with his British adversary that the Revolutionary War would be “carried on agreeable to the rules which humanity formed” and “to prevent or punish every breach of the rules of war within the sphere of our respective commands.” During the Civil War, President Lincoln approved a set of “Instructions for the Government of the Armies of the United States in the Field,” which inspired other countries to adopt similar codes for their armed forces, and which served as a template for international codifications of the law of war.