Unequal treaties have become synonymous with the imperial practice of Western states in East Asia during the nineteenth century. They have also become a popular subject of study for historians of international law. A neglected feature of the history of unequal treaties is the way they were used and theorised upon as instruments of informal empire before the nineteenth century, in the early-modern age. Hugo Grotius in particular wrote extensively on unequal treaties and alliances through his familiarity with the Dutch East India Company’s exploits in the East Indies, where the conclusion of treaties with indigenous rulers formed the cornerstone of Dutch imperialism. This article delves into the early-modern roots of unequal alliances and discusses how the Grotian analysis of unequal alliances influenced other authors of the classic law of nations.