From Adriatic: A Concert of Civilizations at the End of the Modern Age, by Robert D. Kaplan (Random House, 2022), Kindle pp. 36-38:
I look at more maps in my hotel room in Ravenna: those of the greater Adriatic. Rome is eventually replaced by Western Rome and Eastern Rome; then by the Visigoths, the Ostrogoths, the kingdom of Odoacer, and Eastern Rome, all elbowing for territory; then, in turn, by the Arians and the papacy, though by the sixth century the Adriatic is all Eastern Rome. In the early eighth century the division is between the Lombards and Eastern Rome, in the early ninth between the Franks and Byzantium. In the Middle Ages the Normans, Hungarians, and Serbs, as well as the German Empire, Salerno, Naples, and Venice, all gain prominence; until by the late fifteenth century, as the Renaissance reaches full flower, it is Venice facing off against the Ottoman Empire, even as northern Italy is divided among Savoy, Milan, Genoa, Mantua, Florence, and Siena, and southern Italy between the Papal States and the kingdom of Naples.
Later on, all of these polities, too, will become shades: disappearing, literally, into the past. Voltaire said Rome fell “because all things fall.” Indeed, empires are not illegitimate simply because they eventually collapse: the wonder is that so many have lasted as long as they did. Rome’s universal civilization, with its cruel yet rational, i.e., charmed-conservative paganism, ultimately became impossible to sustain in the hinterlands; and Rome’s breakup led to the panoramic migrations, coupled with the religious passions and particularism, that we associate with Late Antiquity and the Dark and Middle Ages, with all of their attendant political-territorial complexity. Still, the geographic breadth of Rome, lasting as it did for so many centuries, remains an astonishment: an imperial domain impossible to imagine reassembled in any form. Only world governance could equal or surpass it.
In sum, the passage from antiquity to Late Antiquity registers a more confused ethnic and territorial map, with the big shifts that merit chapter breaks in history books barely noticed at the time. For example, the deposition in A.D. 476 of Romulus Augustulus by the barbarian Odoacer—an Arian Christian soldier of vague Germanic and Hunnish descent—is commonly marked as the end-point of the Roman Empire in the West, though the event elicits little mention by any chronicler of the era: its significance becomes apparent only much later in hindsight. After all, Odoacer, rather than eviscerate what remained of the empire, actually restored some facade of order and stability to it, even as he reconquered Sicily from the Vandals in A.D. 477 and annexed Dalmatia in A.D. 480. The real break with the classical past occurs only later with the Gothic War of A.D. 535–554, which devastated much of Italy with famine and chaos, and was quickly followed in 568 by the Lombard invasion, so that Italy was at war for more or less seventy years until 605. Italy would never again be united until modern times. The Lombards, a Germanic confederation with a strong Arian element that included Saxons, Gepids, Bulgars, Sueves, and others—a fascinating horde first recorded by Tacitus—truly herald the passage of Late Antiquity into the so-called Dark Ages.