The Westphalian tradition of just war thinking rooted itself in a different understanding of natural law. Instead of understanding natural law as part of the divine law and reflecting humanity’s moral aspirations, the Westphalians’ natural law was rooted in the “state of nature” and reflected what reason and custom told us about humanity’s actual conduct. Justice, in this view, did not include liberality or charity; it involved the protection of the rights of sovereigns. International justice became equated with the rights of sovereign autonomy and reciprocal non-interference associated with the Treaties of Westphalia. The just war thinkers of this era are thus more hesitant to endorse a right of rebellion, intervention to support rebels, humanitarian intervention, war as punishment, war to defend the innocent, or war against those who commit crimes against nature. War is an instrument to defend international borders, not to enforce an abstract ideal of justice. This leads to the signature contribution from the Westphalian tradition: that the preservation of the balance of power is a just cause because it preserves the independence and territorial integrity of every state.