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 modern differences.
By definition the examples are cherry-picked. I noticed he didn't pull up old Visigoth ranges, nomadic farmers or Babylonian borders.
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.
When I was reading through the examples I sort of wondered why sometimes these geopolitical phenomena persist, and other times not.
For example, at one time long ago in the US, politics were dominated by "frontier-interior" versus "urban-coastal" dynamics, and then as the US grew, and the civil war came about, it established a lot of the geopolitical patterns evident today (although I'd argue the urban-rural distinction is maybe reemerged in a more distributed way today).
To explain cherry-picking versus something else, you'd want a theory for why patterns sometimes change and other times remain the same.
I think that often past borders are the consequence of different demographics, which clearly translate into modern differences.