The Crusades were a series of Christian holy wars conducted against infidels—non-believers. The most significant crusade was a massive expedition led by the Roman Catholic Church to recapture Palestine, the land of Christian origins, from the Muslims. Pope Urban II launched the Crusades in 1095 C.E., when he urged Christian knights to take up arms and seize the Holy Land.
After the First Crusade, the Christians captured Edessa, Antioch, and Jerusalem, and divided that territory into feudal states. However, the disorganized Muslim forces reorganized under the leadership of Saladin and retook Jerusalem in 1187 C.E. The Fourth Crusade never made it to the Holy Land. The crusaders, supported by the merchants of Venice, conquered and sacked the Byzantine capital of Constantinople in 1204 C.E. This event severely weakened the Byzantine Empire.
Though the quest for the Holy Land was a failure, it led to great economic developments in Europe; it encouraged trade with Muslim merchants and increased the European demand for Asian goods. As a result, Italian merchants from cities such as Venice and Genoa greatly profited, and Europe was reintroduced to the goods, technology, and culture of the other regions.