Few ideas should be as clear as natural law. A law that is so intrinsic to reality that it is at once obvious and universal has been propounded since the time of Aristotle. And yet, throughout human history there has been constant debate as to its content if not its existence. Because of the lack of a recognized lawgiver in international relations, there has long been a connection between natural and international law. Indeed, the current international system is fundamentally based on a particular definition of “natural law” – but, far from being “natural,” it was the result of a specific set of historical events.

In the Summer 2009 issue of the IJM James Apple described “The Origins of the Modern State System” as deriving from the Reformation, the Wars of Religion, and the Peace of Westphalia that brought them to an end in 1648. But actual treaties of Westphalia, by a demarcation of boundaries and description of responsibilities, did not create this system alone. A corresponding change in political and legal thinking was also necessary.

The Reformation and religious war, especially the Thirty Years’ War (1618-1648) that led to the death of roughly thirty percent of the population of Central Europe, vitiated from European political thought the idea of legal and moral unity that harkened back to the Roman Empire and was embodied in the medieval Catholic Church. The internecine confessional struggle of the 16^th Century discredited the concept of absolute values, leading a group of philosophers to posit a  minimal law of nature. Reflecting on a theoretical state of nature in which humans lived prior to the establishment of society, they agreed that life being the ultimate virtue, self-preservation was the fundamental basis for natural law.

Simple as this may sound, Hugo Grotius, Thomas Hobbes, and others wrangled over the details. While Grotius believed that humans were naturally friendly and generally recognized the obligation not to harm one another, Hobbes perceived that the only true way to assure for one’s own safety in a state of nature was, in fact, to eliminate all threats – thus leading to the “war of all against all” and necessitating a Leviathan to provide order. Differences notwithstanding, this vision of natural law became essential to the Westphalian state system because, just as people in a state of nature were only bound by a minimal natural law because they had no overlord, so states in the international system were only bound to a very few laws minus a global Leviathan.

It was Grotius who first enunciated the idea of the moral equivalency of people in a state of nature and states in the international system, and for this alone he well deserves his epithet as the father of modern international law. However, the minimalism of his law rendered states autonomous and independent agents, beholden only to the covenants to which they freely agreed. Thus, the strict respect for treaty law and state sovereignty inherent in the Westphalian system, although often described as hallmarks of modern positivism, derive in fact from “natural law.”