I would like to kick off this series focusing on one of the most common historical misconceptions, the Crusades. Specifically I will be debunking the motive behind the wars themselves.
The first interactions a major western power had with a major eastern power was the conquest of Hispania (Spain) by the Umayyad Caliphate from the Visigoth Kingdom from 711–788. It is worth noting that the Crusades kicked off around 1096. The Visigoths were a Christian kingdom, and there was no effort made by the church to reclaim Christian land from the Muslim invaders.
The starting point of the Crusades can be linked to one man, Emperor Alexios I Komnenos of Byzantium. The Byzantine Empire was fighting a losing war in Asia Minor against the Seljuk Turks. In an effort to turn the tides of battle, Emperor Alexios appealed to Pope Urban II for soldiers to help reclaim lost Byzantine territory. Pope Urban II, hoping to draw the Byzantine from Greek Orthodox back to Catholicism, called upon the leaders of Europe to begin raising armies.
It should be noted that the first crusade was not sanctioned by the church. In 1906, a French preacher named Peter the Hermit whipped the population of Europe into a frenzy and soon found himself leading an army of 40,000 men, women, and children to the rendezvous point at Constantinople. On their march, the army got hungry, and Peter lost control as his men pillaged their way through Christian Germany, Hungary, and Greece where horrible massacres were committed against local Jewish populations. The attacks were so bad and so condemned by the Church, that many Bishops rode out with their personal guards to defend the local Jewish populations and fight off the crusaders. Nevertheless, the non sanctioned People's Crusade arrived in Constantinople, was ferried across the bosphorus, and promptly massacred by the far more disciplined Turks.
The actual crusade, "The Prince's Crusade," was headed up by five European leaders, mainly from France and Germany. Upon entering Asia Minor they defeated the Turks and managed to fight their way down to Jerusalem, recapturing the city. Although they swore an oath to the emperor and the pope, the crusader kings did not return the land to Byzantium but instead kept it for themselves, forming the Crusader States. The Islamic world would find itself at war with these states for the bulk of the Crusades.
So we have a series of wars over land. That's it. Sure, religious fervor can be used to whip people up, but that doesn't change the facts that the purpose of the Crusades was clearly driven by a desire for land and not the spread of Christianity or diminishment of Islam or vice versa.