Why did the popes seek protection from the Frankish kings after their conflict with Leo III?

The popes sought protection from the Frankish kings primarily because the Byzantine Empire, under emperors like Leo III, failed to provide adequate military support against the Lombard invaders who threatened Rome.12

This shift in allegiance was driven by several factors:

• Iconoclastic Controversy: The imperial policy of iconoclasm introduced by Leo III in 726 caused deep hostility between the papacy and the Byzantine throne. The popes staunchly defended the veneration of images, leading to a significant political and religious rift.314
• Increased Taxation and Neglect: Beyond the religious conflict, the papacy faced increased taxation from Constantinople and a lack of military aid, leaving the church to manage the administration and defense of Rome on its own.12
• Need for a Protector: As the Byzantine government became unable or unwilling to protect papal interests, the popes turned to the rising power of the Carolingian Franks. This alliance, which began with appeals to Charles Martel and was formalized under his successors, eventually secured the papacy and led to the creation of the Holy Roman Empire.315