Dominium mundi

Dominium mundi is an idea of universal dominion developed in the Middle Ages. Inspired by the memory of the Roman Empire, dominium mundi implied the recognition of one supreme authority, which generated a prolonged political and spiritual struggle between imperial and ecclesiastical power. This struggle can be said to have begun with the Investiture Controversy, and was mainly embodied by the Holy Roman Empire and Catholic Church, which elevated the emperor and Pope, respectively, to the status of supreme ruler. The idea of universal dominion divided Italy into the warring faction of Guelphs and Ghibellines. Guelphs supported the Church, while Ghibellines supported the Empire. After two hundred years of division during the 12th and 13th centuries, neither of the powers had prevailed, due to their mutual dependency and the rise of the powerful and practically independent reigns of Church and the State. The idea of dominium mundi did not reappear in its original form, despite the fact that both universal powers subsisted.

At the time of the reign of Frederick I (1152-1190), the imperial idea had already reached maturity. Its continuity was emphasized in Europe from the Roman times, through the Carolingian Empire link. In fact, Frederick I spoke about Charlemagne as the model of emperors and had him canonized in 1165 without the requirements. The thesis on the public sovereignty that Roman law (rediscovered by the European jurists and politicians in the twelfth century) contains were also used in favor of the imperial ideas. It was of them that it was deduced the unicity and the universal character of the Holy Roman Empire, considered "a project of worldwide dominion" that symbolizes the whole period. Given these premises, it was believed in the court of Frederick I that the Empire, established directly by divine will as a form of political organization of humanity, was sacred. The expression Sacrum Imperium appears for the first time in a document of 1157.

...
Wikipedia