A) the desire to find a trade route to Asia
As Christopher Columbus set out to try and find a faster trade route to India, he guided his ships West, expecting there to be open ocean from Europe to Asia, since North and South America were not mapped yet. He landed in the Caribbean, and called the natives "Indians", since he thought he was in India. Four expeditions later, he never landed in North or South America, only the immediate Caribbean Islands / Indies.
After more expeditions to this new land after Columbus, the Americas were soon discovered. (Note: Christopher Columbus did NOT discover America!)