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How did Byzantine iconoclasm affect relations between the pope and the Byzantine emperor?

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Side-by-side maps of central Italy showing the changing boundaries of the Papal States. The left map highlights the Papal States after the Treaty of Vienna in 1815 in green, showing their greatest extent. The right map shows the Papal States' reduced territory just before absorption into Italy, with orange marking areas annexed in 1860 and yellow showing the final area annexed in 1870, centered ar — Papal States The Papal States in 1815 (left) and at their annexation by Italy in 1870.

Byzantine iconoclasm significantly strained relations between the papacy and the Byzantine Empire, acting as a primary catalyst for the political alienation of Rome from Constantinople.12

When Emperor Leo III introduced iconoclasm in 726 and officially prohibited the use of religious images in 730, he did so without papal approval, directly intervening in doctrinal matters. Popes Gregory II and Gregory III vehemently rejected these iconoclastic policies, with Gregory III formally condemning them at a council.3412

This religious conflict, compounded by the Byzantine Empire's inability to provide adequate protection against the Lombards and the imposition of new tax burdens on Italian subjects, drove the papacy to seek a new protector. Consequently, the popes turned to the Carolingian Franks, leading to a historic alliance. This shift culminated in the coronation of Charlemagne as emperor of the Romans in 800, which effectively signaled the papacy's move away from Byzantine political authority and toward a new Western power structure.132