AbstractThis article analyses the arguments posed by Spanish jurists regarding the character and value in international nineteenth-century order of the titles to territories that the Spanish State inherited from the Catholic Monarchs. Focused on defending colonial interests in the Pacific, Spanish jurists insisted upon reproducing the legitimising arguments of the Conquest throughout the nineteenth century, until the German occupation of the Caroline Islands, expressly supported by the agreements reached at the Berlin Conference, forced them to rethink the foundations of their argument. The conflict surrounding the Caroline Islands was the first example of confrontation between articles 33 and 34 of the Act of Berlin and historical titles.