By the middle of the seventeenth century, a category of sovereign princes and polities had succeeded in monopolising jurisdiction over external relations and the internal machinery of government that allows to speak of sovereign state. The Old Regime saw the further emergence, in governmental and diplomatic practice as well as in learned writings of the paradigm of the law of nations as the preserve of sovereigns. As legal practice and literature, it also expanded in scope and mass to new regulatory fields such as the law of the sea, maritime warfare, neutrality or dispute settlement. The great treatises on the law of nations of the middle of the eighteenth century fleshed out the dualist system of law of nature and of nations that formed one of the intellectual backbones to Grotius’ work into an elaborate framework of the governance of international relations inside Christian Europe and for its imperial expansion outside.