The Crusades were a long series of spiritually inspired military campaigns, usually though not always aimed at conquering territory ruled by various Muslim empires. Because of the spiritual nature of the Crusades, popes had a substantial influence in calling for and determining the goals of a Crusade. However, popes would often lose control of the crusaders as various princes and rulers would use the spiritual elements of a crusade for economic and political gain.

The First Crusade

The First Crusade was called by Pope Urban II in 1096 after the Byzantines requested help fighting the Turks. Urban's call was answered by a significant number of European princes, and to ensure his continued influence over the direction of the Crusade, Urban appointed Adhemar, bishop of Le Puy, as spiritual leader of the Crusades. Though Adhemar was instrumental in the early phases, he died of typhus before the Siege of Jerusalem in 1099. When the city was ultimately conquered, the various princes divided the land between themselves.

The Second and Third Crusades

Pope Eugene III called for a Second Crusade in 1145, a call answered by Kings Louis VII of France and Conrad III of Germany. After this Crusade failed and led to the recapturing of Jerusalem by the forces of Saladin, Pope Gregory VIII called for a Third Crusade in 1189. Despite the fact that Richard I of England, Phillip II of France and Frederick I of Germany all participated, the Crusade still failed to retake Jerusalem.

The Fourth Crusade

While the Second and Third Crusades demonstrated the pope's inability to control crusaders despite his spiritual influence in compelling kings to fight, the Fourth Crusade points to a total failure of the pope. In response to the failure of the Third Crusade, Pope Innocent III called for a new Crusade in 1198. The crusaders, however, led by the Venetian army, deviated from their initial target of Egypt and attacked Christian Constantinople, the wealthy Byzantine capital.

Subsequent Crusades

The failure of the Fourth Crusade did not stop popes from attempting to rally the armies of Western Europe under a spiritual banner, though the subsequent Crusades did not lead to widespread participation by the monarchs of Europe as the first few had. This points to a decline in papal influence, which was reflected on a bigger scale, as the power of the Papacy was declining in relation to regional political powers.