After the fall of the Western Roman Empire , Italy was seized by the Ostrogoths ,  followed in the 6th century by a brief reconquest under Byzantine Emperor Justinian . The invasion of another Germanic tribe , the Lombards , late in the same century, reduced the Byzantine presence to a rump realm (the Exarchate of Ravenna ) and started the end of political unity of the peninsula for the next 1,300 years. The Lombard kingdom was subsequently absorbed into the Frankish Empire by Charlemagne in the late 8th century. The Franks also helped the formation of the Papal States in central Italy. Until the 13th century, Italian politics was dominated by the relations between the Holy Roman Emperors and the Papacy, with most of the Italian city-states siding for the former ( Ghibellines ) or for the latter ( Guelphs ) from momentary convenience.