The marriage of Isabella and Ferdinand

Ferdinand of Aragon marries Isabella of Castile in Valladolid, thus beginning a cooperative reign that would unite all the dominions of Spain and elevate the nation to a dominant world power. ... Four years later, Spanish Muslims were handed a similar order

Explanation:

Ferdinand of Aragon marries Isabella of Castile in Valladolid, thus beginning a cooperative reign that would unite all the dominions of Spain and elevate the nation to a dominant world power. Four years later, Spanish Muslims were handed a similar order.

Explanation:

The correct answer is - C) Disease had decimated the American Indian population, and the Caribbean plantations required more workers to perform hard labor.

When the Europeans came to the New World, they didn't just brought their culture, religion, technology, but also they brought diseases. This diseases, that are just an ordinary seasonal thing for the Europeans, were actually fatal for the Native Americans because their immune system was not able to cope with them, so most of them died. The Europeans, at first, wanted to use the natives as labor force, but as they were dying so quickly and their numbers dwindled, they needed new labor force, and they found it in Africa. The stronger African tribes kept lots of slaves, and the Europeans understood this and payed in order to purchase them, the stronger African tribes saw an opportunity to profit, so the business of slave trade started.