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Effects

As with any war of such length, the drawn-out Byzantine–Arab Wars had long-lasting effects for both the Byzantine Empire and the Arab world. The Byzantines experienced extensive territorial loss. However, while the invading Arabs gained strong control in the Middle East and Africa, further conquests in Western Asia were halted. The focus of the Byzantine Empire shifted from the western reconquests of Justinian to a primarily defensive position, against the Islamic armies on its eastern borders. Without Byzantine interference in the emerging Christian states of western Europe, the situation gave a huge stimulus to feudalism and economic self-sufficiency.

The view of modern historians is that one of the most important effects was the strain it put on the relationship between Rome and Byzantium. While fighting for survival against the Islamic armies, the Empire was no longer able to provide the protection it had once offered to the Papacy; worse still, according to Thomas Woods, the Emperors "routinely intervened in the life of the Church in areas lying clearly beyond the state's competence". The Iconoclast controversy of the 8th and 9th centuries can be taken as a key factor "which drove the Latin Church into the arms of the Franks." Thus it has been argued that Charlemagne was an indirect product of Muhammad:

The Holy Roman Empire of Charlemagne's successors would later come to the aid of the Byzantines under Louis II and during the Crusades, but relations between the two empires would be strained; based on the Salerno Chronicle, we know the Emperor Basil had sent an angry letter to his western counterpart, reprimanding him for usurping the title of emperor.