The Crusades were military campaigns generally against the Middle East with the objective to recover the Holy Lands. There were a total of nine important crusades and dozens of unnumbered "crusades" afterwards. The Crusades had a tremendous social, political, religious, cultural and economic impact on the medieval world that frequently manifests itself even today.
The Crusades were often invoked by the Pope who had the power to unite all the Catholic nations against a common enemy. The Sixth Crusade was the exception since it was launched without the blessing of the Pope. At first, this enemy was the Turks who were expanding into the Byzantine Empire's territory. As some threats were dealt with, new objectives to conquer more land were set generally by the Pope or other leaders of the Crusades. Kings and princes often took an active role in directing and supervising their army.