The End of Composite Monarchies: Hugo Grotius’s <i>De iure belli ac pacis</i> and Mid-Seventeenth-Century Iberian Diplomacy

Abstract This article sheds light on the seventeenth-century Catalan, Portuguese and Castilian uses of Hugo Grotius’s De iure belli ac pacis (1625) and, in particular, his chapters on the matter of monarchical succession. By studying the patterns in the ways that Catalan and Portuguese rebels and Spanish diplomats drew on this source to mediate disputes over succession, the article suggests that, while Grotius’s works may have eroded the rights of possession in the Atlantic and the Pacific by building on classical, biblical and Spanish sources, Iberian authors saw the text as a shared rulebook for discussing a sensitive matter that Spain had traditionally resolved through creative ambiguity, by granting and expanding local privileges under the threat of brute force. The article, in this way, encourages a reconsideration of the practical, diplomatic and high-political uses of Grotius’s ideas in Catholic Europe, a reassessment of a clear-cut binary between Dutch ideas of liberty and Spanish visions of empire, and a reconsideration of the historiographical explanation for the decomposition of composite monarchies.