The armies of Christendom during the Crusades were plagued by factionalism, and time and again proved unable to work together or find common interest.

Even in the First Crusade, the armies of Western Europe were quick to break off from their allies in the Byzantine Empire, who they had originally been sent to help. The Latin forces were interested in the reconquest of Jerusalem, achieved in 1099, whereas the Byzantine Empire was keen on recovering their heartland in Anatolia. Bitter ideological differences between Rome and Constantinople, as well as differing goals, effectively prevented any real cooperation between the forces of Byzantium and the Crusader armies. This deprived the forces of Western Christendom of a key regional ally. The diversion of the Fourth Crusade to sack Constantinople in 1204 ended any lingering ideas of unity. The Fourth crusade wasted the resources of Latin troops while dealing a mortal blow to the Byzantine Empire from which they would never recover.

After the rather unexpected success of the First Crusade, a number of Crusader states were established in the Levant, the most important of which was the Kingdom of Jerusalem. These states were bastions of Christian power in the Middle East and key staging areas for future Crusades. However, there were key divisions between those knights and noblemen who had established themselves in the Levant and those who would arrive when the Pope called. The lords of the Crusader states had little interest in contributing to papal expeditions because it was more pragmatic for them to try and coexist with their Muslim neighbours and subjects. This was in stark contrast to the desires of arriving Crusaders, who were wont to upset peace in the Middle East throughout the brief tenure of the Crusader states. A prime example of these tensions boiling over and sabotaging campaigns can be seen in the disastrous Siege of Damascus during the Second Crusade, which saw Christian armies attack what was at the time a neutral city and utterly fail.

Even the oft-romanticized Third Crusade, which was at best a draw, was undermined by infighting within the Crusader camp. Frederick I Barbarossa, Holy Roman Emperor, died en route to the Holy Land and all but his most loyal supporters turned back for Germany. Richard the Lionheart of England and Phillip II of France, once close friends, quarrelled while in the Holy Land and Phillip would also leave with most of his army and return home. The Fifth Crusade again saw papal officials argue with the King of Jerusalem, John of Brienne, and the Siege of Damietta (1219) ended in failure as the armies refused to work together.

Issues of leadership and of incompatible goals/personalities would compound with logistical issues to seriously hamper any efforts by the Crusaders to prop up the dwindling forces of Jerusalem. The Fall of Acre in 1291 signalled the end of the Kingdom of Jerusalem, the Crusader states, and basically the whole thing. Muslim forces were decidedly better organized and motivated by this point, and further attempts to establish a foothold in the Levant would have been fruitless.