In this article Mare liberum is placed within the context of seventeenth-century European politics. It focuses on the development of conventional relations between European States regarding their interests outside of Europe and their importance concerning the status of Asian and African 'actors'. It turns out that in spite of Mare liberum's high-sounding proclamation of equality of non-European sovereigns with European States, Grotius's position as well as Dutch policy was inspired by self-interest and was essentially opportunistic. The Dutch Republic – as well as other European States – used the 'liberal' principles of Freedom of trade and the Universality of the Law of Nations to attack the Portuguese/Spanish claims of monopoly. However, as the Dutch Republic, Great Britain and France developed their own 'Spheres of Interest' in Asia, Africa and the Americas, they effectively excluded would-be competitors. Indeed, in the eighteenth century the 'pacte colonial' constituted a distinctive characteristic of the conventional and customary 'European Law of Nations'. As non-European political actors in the eighteenth century relatively lost military and political power, the European States finally relegated them to an inferior position, beyond the charmed circle of full 'subjects of Public International Law'. The article also is a contribution to the ongoing discussion about the relation between European imperialism and the development of the doctrine of European International Law.