Isabella was queen in fact as well as in name. Under the feudal system, the husband of an heiress was so completely lord of the fief that, in the Capitulations of Cervera, January 7, 1469, which preceded the marriage, the Castilians carefully guarded the autonomy of their kingdom and Ferdinand swore to observe the conditions.[54] Yet, on the death of Henry IV, he imagined that he could disregard the compact, alleging that the crown of Castile passed to the nearest male descendant, and that through his grandfather, Ferdinand of Antequera, brother of Henry III, he was the lawful heir. The position was, however, too doubtful and complicated for him to insist on this; a short struggle convinced his consummate prudence that it was wisdom to yield, and Isabella's wifely tact facilitated submission. It was agreed that their two names should appear on all papers, both their heads on all coins, and that there should be a single seal with the arms of Castile and Aragon. Thereafter they acted in concert which was rarely disturbed. The strong individuality which characterized both conduced to harmony, for neither of them allowed courtiers to gain undue influence. As Pulgar says "The favorite of the king is the queen, the favorite of the queen is the king."[55]
Ferdinand, without being a truly great man, was unquestionably the greatest monarch of an age not prolific in greatness, the only contemporary whom he did not wholly eclipse being Henry VII of England. Constant in adversity, not unduly elated in prosperity, there was a stedfast equipoise in his character which more than compensated for any lack of brilliancy. Far-seeing and cautious, he took no decisive step that was not well prepared in advance but, when the time came, he could strike, promptly and hard. Not naturally cruel, he took no pleasure in human suffering, but he was pitiless when his policy demanded. Dissimulation and deceit are too invariable an ingredient of statecraft for us to censure him severely for the craftiness in which he surpassed his rivals or for the mendacity in which he was an adept. Cold and reserved, he preferred to inspire fear rather than to excite affection, but he was well served and his insight into character gave him the most useful faculty of a ruler, the ability to choose his instruments and to get from them the best work which they were capable of performing, while gratitude for past services never imposed on him any inconvenient obligations. He was popularly accused of avarice, but the empty treasury left at his death showed that acquisitiveness with him had been merely a means to an end.[56] His religious convictions were sincere and moreover he recognized wisely the invaluable aid which religion could lend to statesmanship at a time when Latin Christianity was dominant without a rival. This was especially the case in the ten years' war with Granada, his conduct of which would alone stamp him as a leader of men. The fool-hardy defiance of Abu-l-Hacan when, in 1478, he haughtily refused to resume payment of the tribute which for centuries had been imposed on Granada, and when, in 1481, he broke the existing truce by surprising Zahara, was a fortunate occurrence which Ferdinand improved to the utmost. The unruly Castilian nobles had been reduced to order, but they chafed under the unaccustomed restraint. By giving their warlike instincts legitimate employment in a holy cause, he was securing internal peace; by leading his armies personally, he was winning the respect of his Castilian subjects who hated him as an Aragonese, and he was training them to habits of obedience. By making conquests for the crown of Castile he became naturalized and was no longer a foreigner. It was more than a hundred years since a King of Castile had led his chivalry to victory over the infidel, and national pride and religious enthusiasm were enlisted in winning for him the personal authority necessary for a sovereign, which had been forfeited since the murder of Pedro the Cruel had established the bastard line upon the throne. It was by such means as this, and not by the Inquisition that he started the movement which converted feudal Spain into an absolute monarchy. His life's work was seen in the success with which, against heavy odds, he lifted Spain from her obscurity in Europe to the foremost rank of Christian powers.