Momentous changes swept Spain in the fifteenth century. A royal marriage united Castile and Aragon, its two largest kingdoms. The last Muslim emirate on the Iberian Peninsula fell to Spanish Catholic armies. And conquests in the Americas were turning Spain into a great empire. Yet few in this period of flourishing Spanish power could define "Spain" concretely, or say with any confidence who were Spaniards and who were not. Speaking of Spain...