What allowed the christian crusaders kingdom to remain until 1291 is the fact that, the Muslims were too divided to conquer the kingdom. The Visiogoths from Spain were able to sent reinforcements. Venice and Genoa used the Kingdom as a trade hub.
One effect of the Crusades was the creation of a new hero for the Islamic world: Saladin, the Kurdish sultan of Syria and Egypt, who in 1187 freed Jerusalem from the Christians but refused to massacre them as the Christians had done to the city's Muslim and Jewish citizens 90 years previously.
