David Bosco writes in Moral Principles versus Military Necessity (The American Scholar, Winter 2008).
During the hot and desperate summer of 1862, a senior American commander found himself consumed with the question of insurgents. Major General Henry Halleck had become general-in-chief of the Union armies in July of that year, and he soon discovered that the army had no laws or regulations to govern its contacts with the bands of irregular Southern forces in the field. A lawyer by training, Halleck found the absence of guidance maddening. Union troops were encountering an array of rebel forces, some uniformed, some not. “The rebel authorities claim the right to send men, in the garb of peaceful citizens, to waylay and attack our troops, to burn bridges and houses and to destroy property and persons within our lines,” Halleck vented in a letter sent on August 6.
Halleck’s correspondent was eager to help. Francis Lieber (1798–1872) was then a professor of history at Columbia College. A Prussian immigrant, he was a military veteran who had recently devoted himself to studying the conduct of war. What’s more, he was a passionate supporter of the Union cause and was keenly ambitious to influence national policy. Less than a year after that first exchange, a short paper Lieber wrote for the general on how international law regards insurgents and guerrillas had blossomed into America’s first code regulating the conduct of its army in warfare.
Lieber’s Laws of War (General Orders Number 100) were published during the Civil War in 1863. The code’s 157 articles presaged the Geneva Conventions and the Law of Land Warfare (or Law of Armed Conflict). Lieber’s story was new to me. I don’t necessarily share all of the author’s conclusions, but the story itself is well worth reading.