It doesn't sound to me like you have engaged with TSR's DnD rules.

Basic Expert Companion Masters System (and especially the Moldvay Basic and Holmes Expert) all spent good amounts of time on this. Expert and Companion especially. Also summarized on the D&D Compendium. These are the DnD that many Old School games are harkening back to.

1E and 2E DnD did both have substantial material on this. In 2E a lot of social material is in the supplements, especially the grand Historical series.

I know there was a lot of 3E stuff by WorC later, but for me that is not Old School D&D and I frankly skipped it. Back with the game in 4E and 5E. Agreed the theme was not much covered in 4E and the 2014 5E.

I am not sure that this really counts as Mandela effect.