The Second Crusade began in 1147.
Combined Muslim forces dealt a humiliating defeat to the Crusaders, decisively ending the Second Crusade; Nur al-Din would add Damascus to his expanding empire in 1154 ("Crusades").
There were numerous attempts by the Crusaders of Jerusalem to capture Egypt, Nur al-Din’s forces took hold of Cairo in 1169 and forced the Crusader army to evacuate ("Crusades).
Outrage over these defeats inspired the Third Crusade
Pope Innocent III called for a new Crusade in 1198. Power struggles in and between Europe and Byzantium drove the Crusaders to divert their mission in order to topple the Byzantine emperor, Alexius III ("Crusades).
The Fourth Crusade ended with the conquest and looting of the Byzantine capital later that year in 1204 ("Crusades).
Pope Urban II requested Europe to wage war against Muslims because he saw the opportunity to send sinful knights on a spiritual act to regain Jerusalem, which had been taken by the Muslims, to have their violent lives forgiven of the sins they had confessed. This would save them from eternal damnation in Hell, as strongly emphasized by the Catholic Church.
The first crusade was started by Pope Urban II to take back holy land.
It was a huge success so many returned home. The others stayed to govern over crusader states. Combined Muslim forces eventually defeated all of the crusaders.
The Crusades were a holy war between the Christians and the Muslims, in Palestine