text: Yes, Natural Law.  Pufendorf and Grotius made this clear.  Don't forget that until fairly recent times, Natural Law held the dominant place in legal theory.  It is the basis of Catholic moral theology, the basis of the legal thinking of Blackstone, our Founding Fathers ("We hold these truths to be self-evident, . . . that they are endowed by their Creator . . ."), Montesquieu, Locke, Aquinas, etc. etc.  Even in your own thinking, you appeal to Natural Law.  Your opposition to Jim Crow laws (positive law) is that it they are unjust.  You correctly believe that if a positive law is "unjust" --- "just" being defined by reference to something higher than man-made law --- it is no law at all.  The founders of international law believed the same way.