Limits

John Fabian Witt explains how the Emancipation Proclamation led directly to new rules restricting the behavior of armies at war:

.... Drafted by the Columbia professor Francis Lieber and approved by Lincoln himself, the code set out a host of humane rules: it prohibited torture, protected prisoners of war and outlawed assassinations. It distinguished between soldiers and civilians and it disclaimed cruelty, revenge attacks and senseless suffering.

Most of all, the code defended the freeing of enemy slaves and the arming of black soldiers as a humanitarian imperative, not as an invitation to atrocity. The code announced that free armies were like roving institutions of freedom, abolishing slavery wherever they went. And it defended black soldiers by insisting that the laws of war made “no distinction of color” — indeed, mistreatment of black soldiers would warrant righteous retaliation by the Union.

The pocket-size pamphlet quickly became the blueprint for a new generation of treaties, up to the Geneva Conventions of 1949. Strong nations like Prussia and France had long suspected that law-of-war initiatives were little more than maneuvering by weaker countries and closet pacifists hoping to make war more difficult. Lincoln’s code broke that diplomatic logjam: It contained no hidden European agenda, and no one could accuse the Lincoln administration of trying to hold back strong armies. ....

The rules of armed conflict today arise directly out of Lincoln’s example. They restrain brutality. But by placing a stamp of approval on “acceptable” ways to make war, they legitimate terrible violence. The law does not relieve war of all its terrors; it does not even purport to. But it stands as a living reminder, a century and a half later, of how thoroughly the United States’ most significant moment still shapes our moral universe. [more]

War and the Emancipation Proclamation - NYTimes.com