Why did the Peace of Westphalia help end widespread enslavement of prisoners of war in Europe?

The Peace of Westphalia (1648) is widely recognized as marking the end of the era of widespread enslavement of prisoners of war in Europe because it established the practice of releasing captives without requiring ransom.1

Prior to this period, defeated enemies were frequently killed or enslaved, and captives were often treated as chattel or movable property. While legal philosophers like Hugo Grotius had previously advocated for exchange and ransom over enslavement, the 1648 settlement solidified a shift in the law of war. This transition reflected a growing moral consensus that in war, the destruction of life or property should not exceed what is strictly necessary to resolve the conflict. By facilitating the release of prisoners without ransom, the treaty helped move European military conduct away from the dehumanizing practice of enslavement, setting a precedent for the more humane treatment of captives that would continue to evolve in international law.1