I’m sceptical, it’s too easy to cherry-pick data to make it look supportive of one’s political agenda. Not saying it’s the case here, I just wouldn’t trust too much "obvious" patterns and easy to understand maps from a twitter thread. More often than not, such threads are omitting data that doesn’t support the view of the author. Reality is rarely obvious and simple.
I totally assumed the examples to be cherry picked but it's still fun to look at. Not every past border is visible on modern maps, but still some are clearly the consequence of those, for example the german maps where the old GDR is the reason for the high rate of atheism or popularity of more extreme parties. I think that often past borders are the consequence of different demographics, which clearly translate into…
That doesn't take away from the insight that certain political histories still resonate today.
Just as you can find examples of geologic features (like mountain ranges or rivers) influencing political divides, so too can you find examples of geologic features not influencing them. Doesn't mean the former is "misleading" or something.