I stopped trying to find out why each civilization failed in Wiki because it’s not always clear and historians bicker over it, though it’s clear drought, invasions, civil wars, and famines played a role in most of them. Yet what’s seldom mentioned is that deforestation (Perlin “A forest journey”) and topsoil erosion (Montgomery “Dirt: the erosion of civilization”) were often the main or one of the key reasons for collapse.
But what’s clear is that societies always collapse, and our civilization will fail as well, since it depends on a one-time only supply of fossil fuels.
Kemp, L. 2019. Are we on the road to civilization collapse? Studying the demise of historic civilisations can tell us how much risk we face today says collapse expert Luke Kemp. Worryingly, the signs are worsening. BBC
In the graphic below, I have compared the lifespan of various civilizations, which I define as a society with agriculture, multiple cities, military dominance in its geographical region and a continuous political structure. Given this definition, all empires are civilizations, but not all civilizations are empires.
Civilization [Duration in years]
- Ancient Egypt, Old Kingdom  The power of pharaoh gradually weakened in favor of powerful nomarchs (regional governors)…. The country slipped into civil wars mere decades after the close of Pepi II’s reign. The final blow was the 22nd century BC drought in the region that resulted in a drastic drop in precipitation. For at least some years between 2200 and 2150 BC, this prevented the normal flooding of the Nile. The collapse of the Old Kingdom was followed by decades of famine and strife.
- Ancient Egypt, Middle Kingdom 
- Ancient Egypt, New Kingdom  Egypt was increasingly beset by droughts, below-normal flooding of the Nile, famine, civil unrest and official corruption
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