Final answer:
Charlemagne distrusted the pope's motives in crowning him Holy Roman Emperor because it could imply that his power came from papal approval, potentially undermining his own authority and provoking tensions with the Byzantine Empire.
Step-by-step explanation:
Charlemagne may have distrusted the pope's motives in crowning him as Holy Roman Emperor due to the complex political and religious landscape of the time. By crowning Charlemagne, Pope Leo III asserted the power of the papacy to confer legitimacy on secular rulers while simultaneously strengthening his own position. Charlemagne, having already secured his power and expanded his empire through military conquests and strategic alliances, understood the implication of being crowned by the pope — it could suggest that his authority derived from papal approval rather than his own right of conquest and governance. This crowning raised questions about the sovereignty of secular rulers concerning papal authority, a conflict that would continue to shape the relationship between the Church and the state throughout medieval Europe. Furthermore, Charlemagne's coronation by the Pope could be seen as usurping the authority of the Byzantine Empire, which still claimed continuity with the Roman Empire. This act could have been perceived by Charlemagne as potentially provoking diplomatic tensions with the Byzantine emperors, who already viewed the power of the Franks with jealousy.