Conquistadors in the Old and New World explains why 15th-century Spain had a ready supply of adventurous young warriors willing to travel overseas and conquer Indian lands:
1492 was perhaps the most momentous year in all of Spainish history. Under the leadership of Ferdinand of Aragon and Isabella of Castile, Spain was united for the first time in 800 years and the last of the Moors had just been sucessfully defeated at Granada. In this same year under the urging of Torquemada, master of the Inquisition, an edict had been issued expelling the Jews from Spain. In addition, after six long years of waiting around the periphery of the royal court, Christopher Columbus had finally been given permission to set sail westward to search for the riches of the east Indies. The Conquistadors who followed in the footsteps of Columbus, were unique products of Spanish histroy which led up to this moment in time. As a breed of men Conquistadors were not new to Spain — indeed they had been part of her culture for almost 800 years. Until 1492 Spain had been constantly at war since 711 AD. In that year Islamic hordes swept out of north Africa from across the Gibralter straits and within seven years had conquered all but the northwest coastal region and marched on across the Pyranies into France where they were finally stopped. The Moorish invaders conquered in the name of the Prophet and in spite of much bloodshed brought to Spain the culture of the Middle east. Their knowledge of irrigation methods opened up arid lands for agriculture andeducation, mathmatics, science and the arts flourished.
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This fervent religious crusade of Christian against Moslem had taken 800 years to complete and the centuries of constant fighting had created a pool of soldiers and a mounted nobility that were little more than warlords. These men born to the saddle and the sword and acustomed to booty and living off the land, still burnedwith the wild religious fervour that had led to the victory over the Moors. When in 1492 the last battles had finally been won, conquistadors of the Spanish crusade were suddenly unemployed. These were men with little to lose and much to gain by adventuring in the New Worlds encountered by Columbus.