Cut off from the world by the Pyrenees and the still unnavigated ocean, broken up into small kingdoms, largely absorbed in their quarrels and in the reconquest of the land from the Saracens, Spain for many centuries played a comparatively small part in the affairs of Europe. Down to 1479 the peninsula contained five independent kingdoms: Castile, with Leon, occupying 62 per cent, of the entire surface; Aragon, with the kingdom of Valencia and the principality of Catalonia, occupying 15 per cent.; Portugal 20; Navarre 1; and Granada, the last stronghold of the Saracens, occupying 2. The marriage (1469) of Isabel, daughter of John II of Castile, with Ferdinand, son of John II of Aragon, united the two branches of the House of Trastamara, and merged the claims of husband and wife to the Crown of Castile. Isabel succeeded her brother, Henry IV, in 1474. Ferdinand, who had already received from his father the Crowns of Sicily and Sardinia, inherited in 1479 the remaining dominions of Aragon. Aragon and Castile remained distinct, each keeping its separate laws, parliaments, and fiscal frontier. Isabel, as queen in her own right, retained the Crown patronage and revenues within Castile, but general affairs were transacted under a common seal. In Aragon Ferdinand's authority was not shared by his queen. The Spanish possessions in Italy belonged to Aragon exclusively, as America afterwards belonged to Castile. A common policy, and the vastly increased resources of a kingdom uniting under its sway 77 per cent, of the peninsula, at once gave preponderating weight at home. During the greater part of the sixteenth century Spain was the chief Power in the world. The half century from 1474 to 1530, which witnessed the rise of this Power, may be subdivided into periods distinguishable as that of organisation and reconstruction, 1474-1504; that of lawlessness and revolution, 1504-23; that of absolute monarchy, 1523-30.
The reforms of Ferdinand and Isabel, "the Catholic Kings," put an end to anarchy, and formed the bridge between the division of power of the Middle Ages and the absolute monarchy of the sixteenth century.