Most people complain about Constantine I the Great because he thoroughly changed the church from being a persecuted movement to being a sponsored religion (Edict of Milan 313). Both before and after that the whole church called itself catholic and orthodox and was led by the Pentarchy (Rome, Constantinople, Jerusalem, Antioch, Alexandria). Using those two names "catholic" and "orthodox" to define the split church after 1054 was semantic because they both claimed the same heritage and both want to unite someday on what they say the original principles should have been.

Thank you for explaining the sources there. When you're looking at about 200-450 it would make sense that individual powerful Romans sought refuge in those lands that became tribes like the Goths, as there were many emigrations over the whole period. I don't know of any strands retaining power that we can be specific about, as the nobility system remained within the city, not without. When we see the individual tribes asserting themselves like Goths (themselves divided) and Heruli, I don't know of evidence that they had absorbed much power from imperial citizens.

Certainly the greater currency degradation on the west side contributed to the loss; and the multiple attempts to declare it a formally dual empire could be said to have fared as well as the Civil War, with a similar pretense of unification, except that unlike us they also lost lots of territory to upstart kings. Once Rome fell in 476 the sole remaining emperor, Zeno, was stuck with holding what meager territory he could retain in the west (largely retaken by his successor Justinian), and I saw some good new data on that today that I wasn't aware of but don't have that page handy for summary. But you're right that tracing this period is a challenge; Huns don't keep good records.

So we had these various tribes compete for centuries until in 800 Charlemagne had amassed so many duchies and territories for the Franks that the Pope decided to get a crown and award it to him, literally as a surprise Christmas present, creating the new concept "Holy Roman Empire" as if it were the rightful heir of the Western Roman Empire 300+ years back. Before then it was just the Frankish kingdom like the Saxon or any other kingdom, allied with the recently created Papal States, but it was the clever name that gave it more push to amass more central European princedoms. To trace the actual de facto power over the city of Rome 476-800, it's that chain I've outlined: Romans, Heruli, Ostrogoths, Byzantines, Lombards, Franks, and Romans again. The de jure power largely follows this but the Byzantines claim credit for overseeing some of the more local tribes.

Now for new info on the later period, I find that Habsburg Castle was built by Count Radbot in 1020 (hawk's burg), and his house dates from that time and became the power brokers of Austria and thus the HRE within about 200 years. But just like the Rothschilds you can only say there was an early long-attested family, over a period of a generation or two they cornered a market and centralized power, and they retained that a long time after. I don't know the details. Time and chance happen to them all. Today Musk, tomorrow someone else. It's great if we can find ties that suggest connections from one power center to another, but for them to be true transfers of power they must be either somewhat similar to the popular narrative or so secret as to be speculative. It's not that important who got what from whom, it's more important which were satanists and which weren't. Obviously this period corresponds to the Dark Ages of greater economic disparity, profligacy and poverty.

Napoleon wanted to start his own empire and succeeded in breaking up the HRE 1798 by overpowering military conquest. Napoleon's name literally means Apollyon, not that he was necessarily an antichrist, but that he did want to be the central power. He got that power through the societal class collapse of the French Revolution and its anarchy leading to a call for a dictator; but like Hitler he bit off too much, made too many enemies, and was defeated by their alliance 1815. (We can certainly say the Rothschilds were involved, because Nathan made a ton of money withholding the news of Wellington's victory until he could buy tons of cheap stock from doomers; he and his brothers had mastered intel networking and so he knew about the victory before any other trader, suggesting that he also had an interest in having assisted the British and Prussian victors.) But Germany having been left a shambles it went through another crazy series of political redefinitions including the Second and Third Reichs until defeated by the Allies in 1945.

Napoleon makes a fictional cameo in The Count of Monte Cristo, filmed with Jim Caviezel. The story, like Ben-Hur, illustrates how easily a nobody can rapidly inherit the power of a titled house and take his own place in society to set things right as he sees fit. And I see that theme repeatedly in history except that the heirs are so rarely noble.