Actually, a major reason why the crusades failed was that negotation and carefull threatment of prisoners was ideologically impossible for the Crusaders, which was not so much the case for the Muslim forces. Whenever the Christians negotiated (like f.e. Frederick the second of Hohenstauffen, you may want to read a bit about him here (Frederick II, Holy Roman Emperor - Wikipedia, the free encyclopedia) they could make momentary gains but would reduce their own militancy, reducing their military potential long term.