Cuius regio, eius religio

Cuius regio, eius religio is a Latin phrase which literally means "Whose realm, his religion", meaning that the religion of the ruler was to dictate the religion of those ruled. At the Peace of Augsburg of 1555, which ended a period of armed conflict between Roman Catholic and Protestant forces within the Holy Roman Empire, the rulers of the German-speaking states and Charles V, the Emperor, agreed to accept this principle. It was to apply to all the territories of the Empire except for the Ecclesiastical principalities, and some of the cities in those ecclesiastical states, where the question of religion was addressed under the separate principles of Reservatum ecclesiasticum and Declaratio Ferdinandei.