After the fall of the Western Roman Empire, Italy fell under the power of Odoacer's kingdom, and, later, 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 the rump realm of the Exarchate of Ravenna and started the end of political unity of the peninsula for the next 1,300 years. Invasions of the peninsula caused a chaotic succession of barbarian kingdoms and the so-called "dark ages". 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 with the former (Ghibellines) or with the latter (Guelphs) for momentary convenience.