A David Graeber inspired study!?
In case you haven't heard of it: https://en.wikipedia.org/wiki/The_Dawn_of_Everything
In case you haven't heard of it: https://en.wikipedia.org/wiki/The_Dawn_of_Everything
A very good example comes from India itself i.e. "The Paradox of Indian History" which is the dichotomy between Archeological Evidence (Indus Valley, Ashoka's inscriptions etc.) vs. Literary Evidence (Puranas, Itihasas etc.) Add to this the linguistic diversities, group/ethnic diversities and successive waves of invasions and displacements and it is enough to drive a Historian mad/happy depending upon how you look at it. The literary/linguistic evidence paints a picture of very advanced societies while the archeological evidence paints a distinctly different but again advanced societies.
Hence studies like the OP's submission are very much needed and welcome.
They became extinct.
To an "educated", emotional mind guarded in a safe place, economic prosperity, the tenets of equality might show promise, but, they might ultimately be sans utility when seen from the lens of survival, thriving, etc.
“Barbarism is the natural state of mankind. Civilization is unnatural. It is a whim of circumstance. And barbarism must always ultimately triumph.”
Here by "Civilzation" i mean explicitly; philosophical ideas/frameworks, societal beliefs/structures/traditions etc. far beyond what is needed for mere survival. For example, Buddhism took the idea of Ahimsa from Hinduism (where its limitations were known) and turned it into the utopian idea of complete non-violence which was then made state policy in kingdoms of North India and current-day Pakistam/Afghanistan. The result was that they fell easily to the islamic barbarians who played by a different set of rules.
What we need is Civilization but with the necessary Barbaric tendencies assuring survival (i.e. procreation and societal self-defense) still maintained.
Note here that this idea has been corrupted by western countries during their colonial rule time period. So you have to be careful to disambiguate legitimate ideas from overt/covert racism.