Very disappointed with this, and I think it is part of a general trend with the 'very short introduction' series - they are often not introductions at all. The language of this is tortured and unsuitable for a general reader who isn't used to the funny way academics write for each other. It assumes a lot of knowledge. I think it's partial too. That might seem odd in the context of a book about the Crusades, but as the author himself points out, they are a live issue now. The book 'The Crusades through Arab Eyes' doesn't make it into the bibliography, and neither does that perspective, though we hear that the Outremer lords weren't any worse than their Turkish equivalents. There is some interesting stuff about the doctrine of Holy War and Just War, and its origins in the Old Testament and Roman Law.
I note in passing that he thinks the Crusades left no permanent legacy in the region apart from the monumental - the various castles. I'm no expert but I wonder if that is true in terms of the genetics of the Palestinian population (quite a few blue-eyed Palestinians) or the practices of the local Christians.