Final answer:
During the Fourth Crusade, the Crusaders attacked Constantinople under the influence of several factors. These included the plea of the Byzantine emperor for a crusade to rescue the Greek Orthodox Christians from the Ottoman Turks, internal politics of the Byzantine Empire, and the Crusaders' attempt to appoint a pro-crusader emperor and control the Byzantine church.
Step-by-step explanation:
The Crusaders attacked Constantinople during the Fourth Crusade under the influence of several factors. Firstly, the Byzantine emperor's plea for a crusade to rescue the Greek Orthodox Christians from the Ottoman Turks led Pope Boniface IX to call for a crusade. Roman Catholic knights from throughout Europe responded to this call. Secondly, the internal politics of the Byzantine Empire played a role as well. The Crusaders became involved in these politics and attacked Constantinople, sacking the city. They attempted to put a pro-crusader emperor on the throne, resulting in a deep betrayal of the Greek Christians and crusading ideals. Lastly, the Crusaders appointed their own priest as the Patriarch of Orthodox Christianity, thus putting the Byzantine church under the control of someone loyal to the papacy.