Answer:
They were free to do so after capturing Granada, is the correct answer.
Step-by-step explanation:
The Spanish kingdoms of Castille and Aragon were united when King Ferdinand and Queen Isabella got married. After the unification, they were searching for national heritage. They wanted to have a fast route for trading in Asian spices which could make Spain rich and powerful and if any other materials were obtained from the voyage it would have been an added benefit.
As compared to other European nations Spain was poor and didn't have many natural resources, colonization was a way in which they could build wealth. Earlier the King and Queen were occupied in fights against the Moors in southern Spain and after the defeat of the moors, they were able to pay attention to other issues.
So when Columbus approached the Spanish king and queen they agreed to finance his voyage and provided him with money and ships.