Stanford Murrell writes, in his book, "A Glorious Institution: The Church in History" (copyright 1998, Chapel Libray)
Could a case be made that the Roman Empire existed until 1870, albeit in a ecclesiastical form of government?"One notable Frankish monarch was Clovis, who converted to Christianity in 496. Clovis was a strong and influential ruler. However, his descendants were not. This fact allowed Pepin III (Pepin the Short, c. 714-768), to rise to power. Pepin was the son of Charles Martel. He deposed Childeric III, the last of the Marovingian dynasty, to establish his own, the Carolingian dynasty. Pepin put Childeric in a monastery and then assumed the throne.
Looking for ecclesiastical approval for all his actions, Pepin received it when he was anointed by Archbishop Boniface in 752 and again by Pope Stephen II in 754. By reviving an Old Testament practice recorded of the Davidic monarchy (1 Samuel 16:13), Pepin symbolically placed the State beneath the authority of the Pope. The precedent was set to believe that the pope had the right to give kingdoms and to take them away. The State had become subservient to the Church.
Within this new religious and political context, Pope Zacharias (d. 752, the last of the Greek popes, 741-752) did not hesitate to ask Pepin to help bring stability to the Lombards, who were still perceived to be a threat to papal power and safety. Pepin agreed to help. He marched against the Lombards and forced them to relinquish much of their territory to the pope, thereby beginning the States of the Church (also known as the Papal States). The pope now held not only ecclesiastical power, but secular power as well. He would do so until 1870, when the new Kingdom of Italy was established."