By the middle of the fourteenth century, Christian control of the Iberian Peninsula extended to the borders of the emirate of Granada, whose Muslim rulers acknowledged Castilian suzerainty. No longer threatened by Moroccan incursions, the kings of Castile were diverted from completing the Reconquest by civil war and conflicts with neighboring Christian kings. Mindful, however, of their traditional goal of recovering lands formerly ruled by the Visigoths, whose heirs they claimed to be, the Castilian monarchs continued intermittently to assault Granada until the late fifteenth century. Matters changed thereafter, when Fernando and Isabel launched a decade-long effort to subjugate Granada. Utilizing artillery and expending vast sums of money, they methodically conquered each Nasrid stronghold until the capitulation of the city of Granada itself in 1492. Effective military and naval organization and access to a diversity of financial resources, joined with papal crusading benefits, facilitated the final conquest. Throughout, the Nasrids had emphasized the urgency of a jihad waged against the Christian infidels, while the Castilians affirmed that the expulsion of the "enemies of our Catholic faith" was a necessary, just, and holy cause. The fundamentally religious character of this last stage of conflict cannot be doubted, Joseph F. O'Callaghan argues.