International law exists in the slippery zone between abstract speculation on binding principles and realistic deference to power. The position of Hugo Grotius as ‘father’ of international law, this article will suggest, results from the way later lawyers have appreciated his suggestion that when human beings enter that zone, they will discover a tendency to subordinate themselves to ‘rules’ that is lacking from other living creatures. Grotius then uses this assumed tendency to explain the trust and confidence with which members of good societies agree to live in peace and expect mutual benefits from cooperating with each other. The same tendency also entitles them to punish those who question the beneficial nature of these rules or lay down obstacles to their expansion. The importance of Grotius in the history of legal thought is highlighted by the manner in which the idea (though not the expression) of the ‘rule of law’ emerges in De iure belli ac pacis (1625) as a powerful justification of the government of a post-feudal, commercial state.
Recent trends such as the turn to the history of international law, the parallel turn to the international law of history and the resulting emergence of international legal history as a field of study have encouraged an unprecedented interest in methodological questions in international legal history. Should international legal historians focus on the specific or the general? Should their narration be accessible to the many or should it be academic and addressed to the few? This article contributes to these emerging debates by focusing on the perspective and scale of analysis and investigating whether micro-historical approaches can help international legal historians to bridge the gap between the academic realm and the public, unveil unknown or little known international legal histories and contribute to the development of the field. This article aims to start a discussion on perspective and scale in international legal history and argues for inclusive and pluralist approaches by drawing out the advantages and potential of micro-history in relation to, and in combination with, the prevalent doctrinal, institutional and diplomatic macro-histories of international law.
Today, the contribution by Gottfried Wilhelm Leibniz (1646–1716), the last ‘universal genius’, to the theory of international law is nearly forgotten. Leibniz was a lawyer by training (later in life holding prestigious positions such as Reichshofrat), and he acted as a diplomat and political advisor to the Duke of Hanover. His engagement with legal practice distinguishes Leibniz from other philosophers. Always looking for intellectual synergies, Leibniz integrated his knowledge of (positive) law into his legal theory. He provides the rare combination of an international legal theory that is both grounded in his metaphysics and natural law theory and inspired by his extensive study of the positive international law of his time (Leibniz was the first to systematically collect and analyse historical international treaty law). This article introduces Leibniz’s theory of international law by outlining the different conceptual layers of his notion of ius gentium, by explaining the functions of natural law for positive international law and by showing how natural law can shape the substance of international relations. The three takeaways from Leibniz for contemporary international legal theory are the idea of optimizing pluralism, his ideas on synergies between theory and practice and, finally, his insistence on treating law as ‘legal science’.