Why did Christopher Columbus want to find a shorter sea route to the west?

Columbus was looking for what would later be called the "Northwest Passage". If the earth was round, as Columbus believed, then he reasoned it would be much faster to go west and find a way to the riches in India, than to take the dangerous journey around the tip of Africa. ( There was no Suez Canal in those days.) Of course, Columbus did not realize that there was an entire continent between Europe and Asia that would be in his way. That's why he called the first natives he found in the New World "Indians", because he thought India would not be far away. Ironically, this led to the discovery of the riches in South and Central America which made Spain the most important European nation for centuries after Columbus' voyages,