Are you certain that the civilizations you consider wealthy were not essentially 'equal poverty' with a tiny number of elites of top? From the article: "After the fall of Rome, people actually got taller and healthier". A generic high standard of living for the common people does not necessarily raise conquering armies or monuments to capture the modern imagination. The contrast is mostly against more distributed societies that you might not recognize as 'famous civilizations' per se, perhaps were able to provide better for their inhabitants.

The Yanomami are the most surveyed group that fits this category

Their chief threat is the externalities from industrialization and encroachment from transactional extractionist commercial systems.

You can look at the Hadzabe and the Tarawa also for other examples in extant locales

https://en.m.wikipedia.org/wiki/Yanomami

  Although some Yanomami really have been engaged in intensive warfare and other kinds of bloody conflict, this violence is not an expression of Yanomami culture itself. It is, rather, a product of specific historical situations: The Yanomami make war not because Western culture is absent, but because it is present, and present in certain specific forms. 

Hunter gather

> But what were those stable civilizations in history with high equality again?

The ones that lost to the unstable ones and had evidence of their existence wiped from history -- is my theory. It's why we can't have nice things.

Stable civilizations would not be violent, it's a disadvantage unless one of the unstable civilizations takes on something resembling Dexters code allowing the stable ones to get on with their civilization

Alternate view https://www.sciencedirect.com/science/article/abs/pii/S18799...