Crusades were military expedition undertaken by Christians during the middle ages primarily to recapture Palestine, which they considered a holy land because Jesus lived there.
The First Crusade which lasted from 1096 to 1099 was undertaken following Pope Urban II's call for a crusade.
The crusaders were able to recover the holy city in 1099. The territory won during the crusade was later divided in four parts named County of Edessa, Principality of Antoich, County of Tripoli, and Kingdom of Jerusalem. However the these gains were not long lasting. Other benefits of The first crusade can only be see its impact on art and literature by way of inspiring poets and artists.
Papal claims to supreme authority over the Orthodox Church renewed religious controversy that had earlier centered around icons. Leading Catholic and Orthodox Church officials excommunicated each other in 1054, creating a situation that remained unchanged for over 900 years. Alexius I’s call for military assistance against the Muslims led to the First Crusade, which led to the reconquest of Jerusalem and the creation of the Latin Kingdom of Jerusalem in 1099.
In 1054, a formal break between the obediences of the Orthodox Church and the Roman Church occurred. Following Manzikert, the Comneni were willing to embrace an alliance
with the military powers of the West in order to stem the advance of the Turks. In response to Byzantine requests, the bishop of Rome called the First Crusade. Reckless freebooters entered the empire on the way to the Holy Land. By 1099, the crusaders successfully established the Latin kingdom of Jerusalem. At first overjoyed, the Byzantines came to fear the growing presence of Westerners in the East. Hostility to the West led to anti-Western riots in Constantinople in 1183. In 1204, Byzantine fears were realized when a “crusade” actually captured Constantinople. Although a Byzantine emperor was crowned again in 1261, the empire was fatally weakened. Like Byzantium, the ‘Abbasid Empire fell to external invaders. In 1221, the Mongols from the steppes of Asia under the leadership of Genghis Khan smashed the remnants of Islamic unity. In 1258, Baghdad fell to the horde, and the last ‘Abbasid caliph was executed. The Mongols disrupted the disorganized Seljuq territories before faltering before the defenses of Egypt. When the Mongols withdrew, one of the Seljuq principalities, the Ottomans, began to overwhelm its neighbors. In the middle of the fifteenth century, Constantinople finally fell to the invaders.