From Imperial Spain: 1469-1716, by J. H. Elliott (Penguin, 2002), 2nd ed., Kindle Loc. 955-980:
Medieval Castile had built up a military, crusading tradition which was to win for it in the sixteenth century an overseas empire. But it had also developed another tradition too easily overlooked – a tradition of maritime experience which was the essential prelude to its acquisition of overseas territories. The discovery and conquest of the New World was, in reality, very far from being a lucky accident for Spain. In many respects the Iberian peninsula was the region of Europe best equipped for overseas expansion at the end of the fifteenth century. Although the opening up and settlement of the New World was to be a predominantly Castilian undertaking, the enterprise had a common Iberian foundation. Different parts of the peninsula each contributed their own skills to a common store on which the Castilians drew with such spectacular results. The medieval Catalans and Aragonese had acquired a long experience of commercial and colonial adventure in North Africa and the Levant. The Majorcans had established an important school of cartography, which had devised techniques of map-making invaluable for the charting of hitherto unknown lands. The Basques, with the experience of Atlantic deep-sea fishing behind them, were skilled pilots and ship-builders. The Portuguese had played a predominant part in the perfecting of the caravel, the stout, square-rigged vessel which was to be the essential instrument of European overseas expansion in the late fifteenth and sixteenth centuries.
But the Castilians also had acquired their own commercial and maritime experience, especially during the past two centuries. The growth of the Mesta and the expansion of the wool trade with northern Europe stimulated the development of the ports of north Spain – San Sebastian, Laredo, Santander, Corunna – which as early as 1296 banded together in a brotherhood, the so-called Hermandad de las Marismas, aimed at protecting their domestic and foreign commerical interests in the manner of the Hanseatic League. Similarly, the advance of the Reconquista in the late thirteenth century to Tarifa, on the straits of Gibraltar, had given Castile a second Atlantic seaboard, with its capital at Seville – itself recaptured by Ferdinand III in 1248. A vigorous commercial community established itself in Seville, including within its ranks influential members of the Andalusian aristocracy who were attracted by the new prospects of mercantile wealth. By the fifteenth century the city had become an intensely active commercial centre with thriving dockyards – a place where merchants from Spain and the Mediterranean lands would congregate to discuss new projects, form new associations and organize new ventures. It was Europe’s observation post from which to survey North Africa and the broad expanses of the Atlantic Ocean.
These developments occurred at a time when western Europe as a whole was displaying a growing interest in the world overseas. Portugal in particular was active in voyages of discovery and exploration. With its long seaboard and its influential mercantile community it was well placed to embark on a quest for the gold, slaves, sugar, and spices, for all of which there was an expanding demand. Short of bread, it was also anxious for new cereal-growing lands, which it found in the Azores (rediscovered in 1427) and in Madeira. Like Castile it was inspired, too, by the crusading tradition, and the occupation of Ceuta in 1415 was itself conceived as part of a crusade which might one day encircle the earth and take Islam in the rear.