Final answer:
Columbus convinced King Ferdinand and Queen Isabella to fund his expeditions by aligning his goals with theirs of expanding Catholicism and gaining a commercial advantage over Portugal.
Step-by-step explanation:
Christopher Columbus convinced King Ferdinand and Queen Isabella of Spain to fund his expeditions by appealing to their goals of expanding Catholicism and gaining a commercial advantage over Portugal. Columbus believed that he could chart a westward route to India, which would expand European trade and spread Christianity. After several years of petitioning and the completion of the Reconquista, Ferdinand and Isabella agreed to finance Columbus's expedition in 1492, providing him with three ships: the Nina, the Pinta, and the Santa Maria.