Lieber Code
The Lieber Code (General Orders No. 100, April 24, 1863) was the military law that governed the wartime conduct of the Union army by defining and describing command responsibility for war crimes and crimes against humanity; and the military responsibilities of the Union soldier fighting in the American Civil War (April 12, 1861 – May 26, 1865) against the Confederate States of America (February 8, 1861 – May 9, 1865).