When Isabel and Ferdinand finally defeated their opposition and gained control of Castile, they effectively ended the internal political crisis which had been raging ever since the ascension of the house of Trastámara to the crown of Castile. They now turned their attention to a program of territorial expansion which eventually would become an empire so expansive that it would include colonies located all over the world. After conquering Granada, Ferdinand continued the kingdom of Aragon's long tradition of economic and political interests in the Mediterranean; Isabel made the Indies her own personal imperial project. When Charles succeeded the Catholic Monarchs, therefore, he inherited a collection of kingdoms and colonies in both Europe and America. This situation, combined with his election as Holy Roman Emperor, resulted logically in a preoccupation with the idea of empire on the part of the political thinkers of his court. Since the revival of the Roman legal tradition in the twelfth century, the Hohenstaufen emperors, utilizing the Roman concept of dominus mundi, thought of themselves as lords of the whole world, in an attempt to assert independence from the papacy, which continued to consider the emperor as the pope's secular agent. When Charles was elected emperor, he seemed to be on the verge of turning this idea from de iure to de facto, creating the first worldwide empire, including the Indies.