Pope Urban II launched the First Crusade in 1095 when he received an appeal from Byzantine emperor Alexius I to help ward off a Turkish invasion.[93] Urban further believed that a Crusade might help bring about reconciliation with Eastern Christianity.[94][95] Fueled by reports of Muslim atrocities against Christians,[96] the series of military campaigns known as the Crusades began in 1096. They were intended to return the Holy Land to Christian control. The goal was not permanently realized, and episodes of brutality committed by the armies of both sides left a legacy of mutual distrust between Muslims and Western and Eastern Christians.[97] The sack of Constantinople during the Fourth Crusade left Eastern Christians embittered, despite the fact that Pope Innocent III had expressly forbidden any such attack.[98] In 2001, Pope John Paul II apologized to the Orthodox Christians for the sins of Catholics including the sacking of Constantinople in 1204.[99]