What threat contributed to the formation of the Holy Roman Empire? How was it arranged?

At one time, Emperor Constantine created a Christian state with its center in Rome. After, this idea was continued by the empire of Charlemagne, but by the 7th century the idea was forgotten, and this posed a threat to the church. Therefore, when the German state became stronger, the pope turned to Otto, her emperor, with a request for support and protection. Otto quickly defeated opponents in Italy and was anointed as emperor and ruler of Western Christians.