I just read Hugh Thomas’ Rivers of Gold, about the Spanish empire, and he gives a wonderful leadup to Columbus by describing the campaigns to retake Spain from the Muzlims. His description of the events leading up to the capture of Granada was about as good as it gets. I recommend this book highly.
Isabella won for Christianity a 500 year reprieve against Islam by funding the discovery of the New World, and new trade routes around Islam to Asia. Now that period is over, and the conflict, put on hold since Lepanto, has resumed with the World Trade Center attack.