Re: Please could anybody check this short text
Your grammar is fine -- good, even, which allows me to be a harsher critic on style.
I think you analsys is good, especially the point about his bias affecting his credibilty as an historian. Your last two sentences rock.
However, the style if very redundant and uses a lot of words when fewer would do. See my version, which I kept as close to yours as possible, except for my ruthless deletions.
I am reading The Crusades by Geofrrey Hindley, which gives a brief account of these conflicts. It is heavy reading. The advanced vocabulary and elaborate style make some parts impenetrable. As I am learning English, I treat it as an additional challenge.
For readers unfamiliar with the topic, the book gives a sufficient amount of information. One thing that I find [found?] disturbing is the author's clear negative bias against the Christian side. I have the impression that while he was writing the book, he deliberately strived to create a feeling of disfavour towards Crusaders and the whole idea of Crusades in his reader. The author’s tendentious [I had to look this word up!] manner of showing Christians in bad light is somewhat irritating. He may not like Christianity but it raises doubts about his credibility as an objective historian. It could, however, encourage more ambitious readers to dig deeper into the matter.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.