Final answer:
Increased tensions between the pope and the Byzantine emperor prior to the Great Schism were significantly heightened by the pope's crowning of Charlemagne as Emperor of Rome, which challenged Byzantine authority and political-theological disputes that arose during the Crusades.
Step-by-step explanation:
One major event that increased tensions between the pope and the Byzantine emperor prior to the Great Schism was the pope's crowning of Charlemagne as Emperor of Rome. This act by Pope Leo III in 800 CE was seen as a challenge to the Byzantine Emperor's authority and a direct assertion of papal influence in secular matters. Moreover, the Byzantines felt slighted as this implied that the Byzantine emperor was not the legitimate Roman emperor. This diplomatic insult exacerbated existing theological disputes between the Western and Eastern Churches and contributed significantly to the estrangement between the two powers.
Additionally, Pope Urban II's call to the Crusades and the way the Western forces behaved in Byzantine territory during the Crusades further strained relationships. The Byzantine emperor expected the crusaders to return conquered territories to him, but this did not happen as planned, leading to further discord. The political maneuvering by both sides in attempts to assert dominance or gain support also demonstrates the complex power dynamics of the period. These events and tensions cumulated in deepening the rift that eventually led to the East-West Schism in 1054 CE.