The demise of the Akkadians is generally attributed to Gutian hordes, while the demise of the Sumerians who followed is attributed to over-irrigation causing excess salinity in the soil.
Here, the series producer Jessica Cecil relates the climate disaster that struck the Egyptian Old Kingdom
All of Upper Egypt was dying of hunger to such a degree that everyone had come to eating their children
Four thousand two hundred years ago, the first great civilisation in Egypt collapsed.
The pharaohs of the Egyptian Old Kingdom had built the mightiest legacy of the ancient world - the pyramids at Giza. But after nearly a thousand years of stability, central authority disintegrated and the country collapsed into chaos for more than a 100 years.
What happened, and why, has remained a huge controversy. But Professor Fekri Hassan, from University College London, UK, wanted to solve the mystery, by gathering together scientific clues.
His inspiration was the little known tomb in southern Egypt of a regional governor, Ankhtifi. The hieroglyphs there reported "all of Upper Egypt was dying of hunger to such a degree that everyone had come to eating their children".
The Nile is at the heart of everything
Dismissed as exaggeration and fantasy by most other Egyptologists, Fekri was determined to prove the writings were true and accurate. He also had to find a culprit capable of producing such misery. (I think we may have found the culprit in the meteor.)
Stalactites and stalagmites
"My hunch from the beginning was that it had to do with the environment in which the Egyptians lived." Fekri felt sure the Nile, the river that has always been at the heart of Egyptian life, was implicated.
He studied the meticulous records, kept since the 7th Century, of Nile floods. He was amazed to see that there was a huge variation in the size of the annual Nile floods - the floods that were vital for irrigating the land.
But no records existed for 2,200BC. Then came a breakthrough - a new discovery in the hills of neighbouring Israel. Mira Bar-Matthews of the Geological Survey of Israel had found a unique record of past climates, locked in the stalactites and stalagmites of a cave near Tel Aviv.
What they show is a sudden and dramatic drop in rainfall, by 20%. It is the largest climate event in 5,000 years. And the date? 2,200 BC.
As Israel and Egypt are in different weather systems, Fekri needed evidence of some worldwide climate event to link this to the collapse of the Old Kingdom. And the evidence came out of the blue.
Geologist Gerard Bond, of the Lamont-Doherty Earth Observatory at Columbia University, US, looks for climate evidence in the icebergs of Iceland. As they melt on their journey south, they leave shards of volcanic ash on the ocean floor.
Dry lake
How far they travelled before melting tells him how cold it was. Cores of mud from the ocean floor revealed to him regular periods of extreme cold - mini ice ages - in Europe every 1,500 years, and lasting 200 years. And one mini ice age occurred at 2,200 BC. Gerard's colleague, Peter deMenocal, looked at climate records for the rest of the world at exactly the same time. From pollen records to sand, the story was the same - a dramatic climate change from Indonesia to the Mediterranean, Greenland to North America.
Scientists were confirming everything Fekri believed - severe climate change causing widespread human misery 4,200 years ago, misery we are only now learning about for the first time.
Back in Egypt, Fekri wanted to put the last piece of the puzzle in place. He wanted direct evidence of this severe climate change in the Nile. And he found it drilling cores in a large lake that had been fed by a tributary of the Nile in ancient times.
He discovered in the critical period, as the Old Kingdom collapsed, the lake had dried up completely - the only time in the whole history of this lake that this had happened. At last, Fekri felt he had proved that the writings on Ankhtifi's tomb were really true. It was nature that had driven people to desperation.
The Ancient Apocalypse series begins on BBC Two on Thursday, 26 July, at 2100 BST