Nigel Cliff presents a new look on the beginnings of the age of discovery with a particular emphasis on the journeys of Vasco da Gama. He begins with an overview of the reconquista and the creation of Portugal and then focus on the religious fervor of Christian vs Muslim as the primary motivator that spurred Europe into global dominance.
While his history is excellent, well researched and yet easily readable, I believe he has placed far too much emphasis on the religious factor. The traditional (and I believe correct view) was that Portugal and Spain desired to find the source for the spice trade rather than continue to be dependent on the Istanbul/Egypt/Venice monopoly. Religion was certainly a motivator on both sides for many of the local conflicts, misunderstandings, and even atrocities that occurred on both sides. However this was mainly an economic conflict that forever shifted the balance of power away from the Eastern Mediterranean center since Constantine towards Western Europe.
While the book is definitely worth reading there is not nearly enough validity to convince any unbiased viewer of Cliff's primary premise that Portugal was embarking on a "Crusade".