There are a lot of books on this topic, but the majority of writers I know are Russians, but it doesnt mean that it's not interesting to read them, if you have an access to a vast library you can find some of their books. I Recommend You some books by:
V. G. Yan (the spelling may look like Jan or Ian) -> Chenghiz Khan
or H. Sienkiewich -> The Crusaders; but I think its better to start with Ivanhoe by W.Scott or with "laughing Man" by V.Hugo (I don't know whether this spelling is right - it may also look like "a man who laughs", or smthing of that kind).