Having finally read "A Perfect Heresy", O'Shea's excellent but all-too-brief look into the Albigensian Crusade, I bought this based on the dust jacket synopsis. I found it to be an informative and compelling look at the contacts--both combative and cooperative--between Islam and Christianity throughout the dark ages, medieval era, and beyond. O'Shea's narrative focuses on the subsequent interactions between expanding Islam and embattled (for a time) Christianity in the regions surrounding the Mediterranean, hence the "Sea of Faith" of the title. The story begins with the expansion of Islam in the 7th century following Muhammed's death and finishes with the "final" conflict between Muslims and Christians in the Mediterranean at Malta in the 16th century. In between O'Shea explores many key battles--Yarmuk in AD 636, Manzikert, Hattin, Constantinople, etc., delving into not just the primary conflicts but the various factions dividing each side. An ugly truth glossed over in subsequent legendary accounts on both sides is the fact that in many of these conflicts (and others leading up to them) the two sides were hardly united against their cross-confessional foe. Umayyad vs. Abbasid, Catholic vs. Orthodox Christian, Arab vs. Berber vs. Turk, O'Shea deftly explains the complex back-stories to these near-mythical conflicts.
O'Shea also shines when he explores the "conviviencia" or periods of cooperation and tolerance that also marked Muslim-Christian interactions from 600 onward. Cordoba under the Umayyads and Palermo under the Normans are excellent examples of how these periods of peace produced cultural explosions of phenomenal wealth and splendor, with everything from poetry to science thriving under these conditions.
Overall this is a well-written and well-researched look into a topic of obvious relevance to modern times. If we have any hope of reaching peace in the Middle East, we (and our political leaders) are going to try to figure out how to re-create a metaphorical Cordoba while avoiding a metaphorical Poitiers in places like Iraq and Afghanistan. Anyone looking for a well written and engaging introduction into past interactions between these two faiths that might better help them understand today's conflicts is encouraged to buy this book. I subtracted one star for the many puzzling typos in this edition and for the fact that O'Shea, in his rush to cover such a wide topic and broad time scale, gives short shrift to some of the more prominent personalities involved in these conflicts (Richard the Lionheart, Louis IX, Holy Roman Emperor Frederick II, and Tamerlane just to name a few).