In short, Jesus, son of Joseph, actually lived, worked, preached and converted many to his new religion during his own lifetime in what came to be called the “Holy Land” and was later the heart of the crusader kingdoms. Furthermore, St. Paul established the first Christian community in Antioch in roughly 50 AD. In short, the territories conquered by the crusaders encompassed the very oldest Christian territory on earth. There were Christians in these lands for almost 600 years before Mohammed was even born.
Furthermore, the territories that later formed the crusader states, the County of Edessa, the Principality of Antioch, the County of Tripoli and the Kingdom of Jerusalem, had all been part of the Roman Empire and officially Christianized in the 4th century AD. From being a minority religion, Christianity became the state and majority religion in 325 under the reign of Emperor Constantine, who rebuilt Jerusalem between 325 and 330.
While Hamilton stresses that Jewish synagogues and rabbinic schools existed in many of their towns, contemporary Muslim sources noted with surprise that mosques were allowed to function in the crusader states (albeit not in Jerusalem itself) and Muslim subjects were even allowed to participate in the haj. This was because, as Jotischky notes, “the First Crusade was a war of liberation and conquest; it was not a war for the extermination or conversion of Muslims.” Far from being forced to convert, the Muslim villagers were run by a council of elders who in turn appointed a “rayse” to represent the community to the Christian lord, while all spiritual and social matters were regulated by the imams in the community in accordance with Sharia law! (Jonathan Riley-Smith, Atlas of the Crusades, Swanston Publishing Ltd, 1191, p. 16 among others.)