The World of the Crusades, Christopher Tyerman. Sadly my copy is rife with printing errors where chapters break off and the topic gets muddled (goodreads says this is a problem for many). I will say there is stuff in the book I have not read in any other book on the crusades, especially about the Women Crusaders and their ahem tattoos.
I have Read Tyerman’s 900 page tome God’s War. Tyerman delves deep into the psychology of holy war. The Crusaders were not all religious fanatics, some were looking for a new life in Outremer, (Palestine), tax evasion (a crusader and his lands could not be taxed), others a get out of jail free card (literally, murderers and etc had sentence commuted if they went on crusade), and contrary to common belief, Crucinatius (signed with cross, crusaders) and Mujahideen (Muslim holy warriors) got along more than they fought, there was more periods of pax (peace) than war between 1095-1291 A.D., with Saladin even having to lay siege to Jerusalem because he fought more wars against people of his own faith and they began to question his title of Champion of Islam. There is even the crusade against Christians, The Fourth Crusade, where Western Catholic Crusaders conquered Eastern Orthodox Byzantine Constantinople.
The Third Crusade alone has one of most bizarre scenes, at night the two camps of Richard The Lion Heart and Saladin would come together, party, and be merry, and during day fight each other. Talk about strange.. buddies around the bonefire and enemies under the sun. (Thomas Asbridge, The Crusades: A New History).