The only 'slaughter' I am aware of the Mongols committing was in china, where there was a peasant class, analogous to particularly downtrodden feudal serfs. This underclass were considered to be little more than animals by the Mongols, since they did not behave in any way the Mongols would respect. I believe some records show that the population of China fell dropped by 50 million (about a half IIRC) in the period after the Mongol invasion. Fortunately the Mongols became the established rulers and came to understand social systems better quite quickly.
The reason the Mongols are associated with needless slaughter is that when they arrived in a region that had no experience of them they would proceed in this manner: approach city, say 'Surrender or Die'. The city almost always decided to fight. The Mongols would then capture the city and kill every living thing inside. Then proceed to the next city, which would usually surrender.
The Christians believed, at first, that the Mongols were the armies of a legendary Eastern Christian ruler they called 'Prester John', so they left the Islamic Nations to their fate. Too late they realised their mistake and began to believe the Mongols to be descendents of the legendary giants and cannibals Gog and Magog...
I do not remember ever hearing of the Mongols having a particular dislike of Islam, it seems more likely to me that Islam was not quite as fanatical as Christianity, which always seems to regard other religions as wicked. Islam, after all regards Judaism and Christianity as versions of Islam that favour particular prophetic figures. Thus Islam would be better tolerated by the Mongol rulers. I did not intend to suggest that Christianity was not tolerated by the Mongols, merely that as a religion that stated specifically that all other religions were false and wicked, it was looked upon most unfavourably.
Lockes':
Mongka was the fourth Khan, following Ghengis, Ogedai and Guyuk. His grandfather, uncle and nephew respectively.
Thanks, for the Divine Wind correction, I had forgotten about the extra Japanese dimension. Kami-Kaze does not mean suicide as many people think.
You are correct about Richard, he spent a total of 6 months in England, the Kings of the period considered the (nominally French) lands of Normandy, Aquitaine and Anjou more valuable than their English posessions since they were descendents of the Normans. But Richard did not only spend most of his time away because he was crusading, he actually had less regard for England than the other Plantagenet Kings.
To get on topic: Monotheism follows from Polytheism because only an established civilisation is arrogant enough to believe that the World must have been created by a single divine being as a deliberate act intended to bring about said civilisation. Up until that point, Gods are just great Spirits of nature, capricious and frequently selfish and stupid.