On Christmas Day 800 Pope Leo III placed a crown on Charlemagne in St Peter's, and a western emperor existed again for the first time in three centuries. The institution that grew from it, refounded by Otto I in 962 and lasting until Napoleon forced its dissolution, was never a state in the modern sense. Peter Wilson's history argues against reading it as a failed nation: it was a different kind of polity altogether, a hierarchy of overlapping jurisdictions in which hundreds of principalities, free cities, abbeys and prince-bishoprics held their own rights under an elected emperor.
Its founding quarrel was over who appointed bishops. Because a German bishop was also a territorial ruler with troops and revenues, the question of whether emperor or pope invested him with ring and staff was a question about who governed. Gregory VII excommunicated Henry IV in 1076, the emperor stood barefoot in the snow at Canossa in 1077 to be absolved, and the contest ran another forty five years to the Concordat of Worms in 1122, which split the ceremony: the church gave the spiritual symbols, the emperor the temporal ones.
The compromise did not settle the underlying claim, and emperors and popes went on deposing one another through the Hohenstaufen century. What it did establish was that the two authorities were genuinely distinct, a separation with no equivalent in the Byzantine east.