Who rules the Christian world?

The Latin-Christian Papal Church initially developed under the protection of the Roman emperors. From this close association, the coronation of Charlemagne gave rise to an independent Western Empire, which from the 10th century onwards was reserved for the ruler of the Holy Roman Empire. This unity was shattered by the Investiture Controversy of the 11th and 12th centuries: the conflict over the appointment of bishops necessitated a redefinition of the relationship between ecclesiastical and secular authority and led to differing conceptions of power and rule.