U.S. Department of Defense. Law of War Manual

"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.

After World War II, U.S. military lawyers, trying thousands of defendants before military commissions did, in the words of Justice Robert Jackson, “stay the hand of vengeance and voluntarily submit their captive enemies to the judgment of law” in “one of the most significant tributes that Power has ever paid to Reason.” Reflecting on this distinctive history, one Chairman of the Joint Chiefs of Staff observed that “[t]he laws of war have a peculiarly American cast.” And it is also true that the laws of war have shaped the U.S. Armed Forces as much as they have shaped any other armed force in the world..."
Department of Defense Law of War