The Crusades were religiously and economically motivated military campaigns aimed at conquering the Holy Land from the Muslims. The Byzantine Empire, the eastern successor to the Roman Empire based in Constantinople, played a major part in the Crusades, and though the East-West Schism had divided the Byzantine Eastern Orthodox Church from the Roman Catholic Church in the West, the two maintained good relations. However, after the sack of Constantinople in 1204, Byzantine relations with Western Europeans soured substantially.

The First Crusade

The First Crusade was in many ways a joint venture between the Byzantines and the Europeans. When Pope Urban II called for a crusade in 1096, he was responding to a plea for help from Byzantine Emperor Alexios I, who was having trouble dealing with the Seljuk Turks in Anatolia. During the Second and Third Crusades, the Byzantines and Europeans also maintained friendly relations.

The Fourth Crusade

Yet by the end of the 12th century, this cordiality ended. When Pope Innocent III declared another crusade in 1198, the new crusader princes and their Venetian allies did not sail to conquer Egypt, as Innocent had desired, but rather set their sights on Constantinople, due to a rivalry between the Byzantines and the Venetians. In 1204, Constantinople was sacked and its many riches taken by the conquering crusaders. This crusade served as a turning point in Byzantine-European relations.

The 13th Century

In the wake of the Fourth Crusade, the victors established a Latin Empire in Constantinople, and exiled the Byzantines to the Kingdom of Nicea. Continual wars between the exiled Byzantine emperors and the Latins eventually led to the Byzantine reconquest of Constantinople in 1261. Latin Emperor Baldwin II fled to Italy and tried to convince Charles of Anjou, French ruler of Naples and Sicily, to help him recapture Constantinople. Charles seriously considered attacking before a revolt in Sicily, partly kindled by the Byzantines, diverted his attention.

The Ottoman Threat

Despite re-establishing its capital, the Byzantine Empire struggled to survive, especially against the growing threat of the Ottoman Empire. Pleas from the Byzantine emperors to the pope and to Western European rulers for assistance fell on deaf ears; the days of the First Crusade, when Pope Urban II responded to Alexios I's call for aid, were long gone, soured by the Fourth Crusade and subsequent wars. In 1453, Constantinople fell to the Ottomans, and the Byzantine Empire was finished.