Final answer:
Queen Isabella and King Ferdinand supported Columbus's voyage due to Christian zeal, the potential for wealth, and strategic trade opportunities. They offered him a title and a share of the potential riches in return for finding a new route to Asia.
Step-by-step explanation:
Queen Isabella of Castile and King Ferdinand of Aragon supported Christopher Columbus's plan to find a sea-route to Asia. They were motivated by the potential to spread Christianity and acquire wealth through trade. After the victory over the Muslims at Granada, the Spanish monarchy was eager to expand their influence. Specifically, Queen Isabella was driven by Christian zeal and the hope of great gains for God and Castile, offering Columbus a title of nobility and a substantial share of any wealth he discovered. Columbus's voyage was seen as a strategic move to find an alternative route to Asia since overland travel had become perilous and costly due to the collapse of the Mongol Empire and the dangers associated with plagues.