From Karen Armstrong’s A History of God: The 4,000-Year Quest of Judaism, Christianity and Islam:

[T]he Christianity of the Angles, the Saxons, and the Franks was rudimentary.  They were aggressive and martial people and they wanted an aggressive religion… Soldier saints like St. George, St. Mercury and St. Demetrius figured more than God in their piety and, in practice, differed little from pagan deities.  Jesus was seen as the feudal lord of the Crusaders…: he had summoned his nights to recover his patrimony – the Holy Land – from the infidel… In practical terms, their God was still the primitive tribal deity of the early books of the Bible.  When they finally conquered Jerusalem in the summer of 1099, they fell on the Jewish and Muslim inhabitants of the city with the zeal of Joshua and massacred them with a brutality that shocked even their contemporaries.