The focus of this collection of articles by Donald J. Kagay is the effect of the expansion of royal government on the societies of the medieval Crown of Aragon. He shows how the extensive episodes of warfare during the 13th and 14th centuries served as a catalyst for the extension of the king's law and government across the varied topography and political landscape of eastern Spain. In the long conflicts against Spanish Islam and neighbouring Christian states, the relationships of royal to customary law, of monarchical to aristocratic power, and of Christian to Jewish and Muslim populations, all became issues that marked the transition of the medieval Crown of Aragon to the early modern states of Catalonia, Aragon and Valencia, and finally to the modern Spanish nation.