Shifting Alliances: The Unstable Bond between Castile and Aragon in the Late-Fourteenth Century

As a land born in war, the medieval Iberian Peninsula was composed of polities that fought each other because of religious differences and for territorial aggrandizement. Thus besides the struggles of Christian against Muslim that comprise the reconquest (reconquista), the medieval centuries also witnessed episodes of warfare between Spain’s Christian states. ¹ Wars between the Crown of Aragon and Castile-LeÓn, though sometimes sparked by dynastic rivalries, normally originated with disagreements over tracts of land conquered or to be conquered from the Muslim south. ² Relations were exacerbated by the extremely porous borders that separated the territories taken from Islam. ³ These “regions of peril” were often dominated by marcher lords who played the neighboring Christian sovereigns off one another. ⁴