The Byzantines didn’t last all that long as anything recognizably Roman. By 641 they had lost 75% of their prior tax base.

They pushed out now and again but were largely Greece and Anatolia for much of their history after that.

Recognizably roman to whom? They recognized themselves as roman, as did their peer polities in the region. That's not the only useful answer to this question but it's not a small thing either.

I should have been more precise. I meant in terms of being like the old Roman Empire. More in terms of vastness than anything.

The army for example had dropped about 75% in size by the timeframe I mentioned. And this is only the eastern half of the former empire.

So the empire was a shell of itself in terms of extent.

Would be as if California, Nevada and Oregon lived on as “Western America” in 2400 with continuity of govt. Impressive in some way but also nothing a contemporary from our time would recognize as being “The United States”.

Even the western roman empire wasn't really roman anymore. The emperor was not Italian, not based in Rome, and often with a disdain toward Rome, the vast majority of the army wasn't Italian either.

But the eastern roman empire was probably even less of an empire than it was roman. The definition of an "empire" is to rule over many kingdoms. When you are reduced to your own territory, you really aren't an empire anymore.

> They recognized themselves as roman

They didn't speak a Romance language, for example, under that respect they were certainly not Roman.

Western Romans, esp the elite, had already spoken Greek for hundreds of years at that point, and huge parts of the population of the west spoke Gaulish, Germanic, Celtic etc etc languages for hundreds of years too. So that's kind of a non argument.

Those Gaulish, Germanic and Celtic elements were becoming Romans as a result of them starting speaking Latin/the Vulgata, the same goes for all the peoples living at the periphery of the Empire. If you were still speaking Celt/German or whatever you were not a Roman, you were a barbarian.

In the Italian peninsula the only part where Greek might have still been a thing is of course Magna Grecia, but that’s a special case. Curious of how many Greek graffitis have been discovered in Pompeii.

This seems like an incredibly retrospective view of romanicity tbh. That part of the empire had always spoken greek, and had never afaik been considered less roman for it.

> and had never afaik been considered less roman for it.

That's quite debatable, as those parts (Western Anatolia, present-day Syria, the old Orient as a whole) had always been more advanced from a "civilisational" point of view (compared to Rome, that is), and hence them viewing themselves as Romans first and foremost would have been a "spiritual" demotion.

I didn't say they viewed themselves "first and foremost" as romans, where are you getting that?

I'm pointing out that their using greek didn't count against what they & others considered to be their "romanness" before the western empire fell, so why are you looking at it that way now?

To be honest I'm not really certain what you're trying to claim though so maybe the distinction is useful for your point. But anyway "to what extent & by whose measure were the eastern romans, and later the byzantines, roman" is one of the most active & scrutinized questions of one of the most visible and prestigious branches of historical scholarship.

And the overwhelming scholarly consensus is that they were roman by any standard that applied in their time and most that we can come up with as well. "They spoke greek and weren't roman because of that" hasn't been a serious reputable stance on the subject for a few generations now.

I am not sure how "they couldn't stop it" is an argument against migration being one of the major causes of the fall of the roman empire if not the leading one. Other causes being ineffective tax collection, ennemies adapting and learning from roman military techniques, and a general collapse of will, where the brightest and most capable ceased to want to serve aggressively in the army and administration for glory.

it's an intellectually lazy, blinkered thing to say

the empire had incorporated new peoples for hundreds of years, through both violent conquest and people migrating in

= immigration is the only reason there was an empire in the first place, and that it lasted as long as it did - it's not like the Roman Empire was constituted of pure Latin OG Romans, lol. (heck, even their founding myths were that they were NOT Latins - it took conflicts for Latins to be recognized and gain citizenship)

so you can't just cherry pick a single time germanic peoples migrated in (as they had successfully many times) and say LOOK IMMIGRATION IS WHY THE EMPIRE COLLAPSED, it's ridiculous

and even if you insist on doing that, again, what's the takeaway? if your policy rests on there being no migration, in a world where there is migration and there's nothing you can do about that, it's a bad and doomed policy - successful polities are the ones with the ability to roll with and take advantage of it, not the ones that stick their head in the sand in some misguided attempt to remain static and hermetically sealed off from the world

So what ended the western part, and why didn’t the same thing end the eastern part?

There's no single one "what", but:

Western rome kept feuding with itself and hiring germanic tribes as mercenaries. After a while, the germanic mercenaries were thoroughly trained in fighting western romans, and eventually western rome pissed off germanic mercenaries and lost the resulting war.

Eastern rome didn't have as many germanic tribes as neighbors, and they had less infighting to begin with.

One of the major reasons earlier-rome had so much military success was that they conquered their neighbors before said neighbors successfully copied all their (really quite amazing) military doctrines.

(I am not a historian, don't quote me on this)

Current thinking on immigration seems to be: shoot the migrants until they stop coming.

This is not my opinion. I'm just the observer.