In the earliest days of concerted effort to explore the oceans, the rulers of Spain had been too busy disposing of Muslim Granada and uniting the separate parts of Spain to patronize scientific exploration as the Portuguese had done. But Spanish traders were active, and Spain was growing in prosperity.
When Portuguese mariners found the three groups of Atlantic islands— Azores, Madeira, and Canaries—a papal decree assigned the Canaries to the Crown of Castile and the others to Portugal. Once the marriage of Ferdinand and Isabella had united Aragon and Castile, Queen Isabella wanted to catch up with the Portuguese.
So in 1491, when the fall of Granada seemed imminent, she commissioned Christopher Columbus to try to reach India by sailing west.