Francis Lieber, a Prussian-born American political philosopher and public intellectual, was an internationally recognized authority on international and military law and a key legal advisor to the Lincoln administration during the Civil War. He is best known for crafting the earliest official government codification of the customary laws of war. The Lieber Code, as his text became known, was issued with Lincolnís approval in 1863 as General Orders No. 100 under the title Instructions for the Government of Armies of the United States in the Field. Previously no such formal, comprehensive code existed to guide and constrain the behavior of troops in the field. Lieberís Code for the Union became the basis for subsequent editions of the standard manual for U.S. forces on the laws of war and inspired similar manuals in many European nations. On the international level, the code substantially influenced the development of modern treaties on the conduct of war, including the later Hague and Geneva Conventions. More. . .