How did Columbus get Spain’s backing for his expedition?

Eight years after his alleged Iceland experience, in 1485 Columbus approached the king of Portugal with his idea. The proposal fell flat; not only did the king’s court mathematicians correctly point out that he’d have to sail at least 10,000 nautical miles to reach Cipangu (i.e. Japan; Columbus argued the distance was only 2,400 miles), but the Portuguese court was already all-in on the sail-around-Africa approach—which seemed especially promising at that very moment, as Portuguese explorers had recently discovered the Congo. Rejected, Columbus pitched his idea to several other monarchs or princes—including Ferdinand and Isabella—but none would sponsor his proposed venture. For the Spaniards’ part, they were at that time in the midst of a costly crusade against the Moors of Granada, the last Muslim holdout on the Iberian Peninsula; still, they kept Columbus around and even paid his living expenses for several years. Clearly there was interest there, but the time wasn’t right.

In 1492, he decided to give the Catholic Monarchs another try. In the court of Ferdinand and Isabella, Columbus explained his idea, again, and offered to carry out his expedition under the auspices of Spain. Now the timing was perfect. Granada had just fallen. With the Spanish victory came war booty—the confiscated property of vanquished Muslims and Jews, especially. Flush with newly-won wealth, Isabella yet turned Columbus away again (his plan now was to try the king of France!)…only to call him back a few hours later after some of his supporters at court convinced her to give him another hearing. In the end, the Catholic Monarchs did agree to sponsor Christopher Columbus’s expedition, despite what must have seemed enormous risk. A deal was struck.

What was the deal?

For the Catholic Monarchs: they were to gain sovereignty over any new territories Columbus might discover. Should he be successful, Spain might even overtake Portugal in the race to control Asian trade with Europe.

For Christopher Columbus: he was granted hereditary titles—Admiral of the Ocean Sea, Viceroy of the Indies—and was promised that he could be governor of all the lands he might discover (in the Catholic Monarchs’ name, of course). In addition, he was to personally retain a generous one-tenth of all riches acquired as a result of the expedition. Several Spanish seaports were ordered to help outfit Columbus, and he was granted a loan by the Monarchs, too.