Stephen II (III) is elected pope. This is a time when the papacy is coming under severe pressure from the Germanic Lombards to the north and Byzantine emperors in the east. So Pope Stephen II seeks to counter their power by allying himself with the only people he can turn to: the Franks, led by Pepin the short, Mayor of the Palace of the Kingdom of the Franks. In exchange for recognizing Pepin as King of the Franks he would receive military and political protection.
Thus Pepin becomes not only king but also "Protector of the Church" and proceeds to invade northern Italy to eliminate the Lombard threat to Rome. He doesn't eliminate the Lombards, who continue to be a major force on the Italian peninsula for several hundred years but he does relieve the pressure being put on Rome. Pepin turns a number of territories over to the control of the papacy, now known as the Donation of Pepin.