The sudden collapse of the Assyrian Empire was due to overpopulation and drought, a group of researchers has found.
The Assyrian Empire was the largest empire the Old World had ever seen, functioning as a "mighty military machine" that dominated the ancient Near East – an area that is now Northern Iraq and Syria.
However, within just 100 years, the civilisation had collapsed. The then joint Babylonian and Median forces attacked and destroyed Nineveh in 612 BC and the empire never recovered - the reason for which has been long debated.
Researchers from the University of California, San Diego, and Koç University in Istanbul, Turkey, have now found evidence that suggests climate change and overpopulation led to the Empire's destruction.
"Traditional explanations for the decline of the Neo-Assyrian Empire in the 7th century BC have emphasised the role of military conflict, and especially the destruction of the Assyrian capital, Nineveh, by a coalition of Babylonian and Median forces in 612 BC," the authors wrote.
"However, it remains unclear how the Assyrian state, the most powerful military machine of its age and the largest empire the Old World had ever seen up to that time, declined so quickly."
Published in the Springer journal Climatic Change, researchers compared recently published climate data with ancient text found on a clay tablet. The text – a letter written to the king by a court astrologer – said there had been "no harvest" that year.
Analysis of the area's weather patterns from paleoclimatic records found that this drought was part of a long period of drought that lasted for several years.
Adam Schneider, from the University of California, said: "As far as we know, ours is the first study to put forward the hypothesis that climate change - specifically drought - helped to destroy the Assyrian Empire."
At the same time, the Assyrian Empire was suffering from overpopulation. Society had grown unsustainably large during the reign of King Sennacherib and the Empire was "fatally weakened".
Within five years, Assyria was ravaged by civil wars. "We're not saying that the Assyrians suddenly starved to death or were forced to wander off into the desert en masse, abandoning their cities," Schneider said. "Rather, we're saying that drought and overpopulation affected the economy and destabilised the political system to a point where the empire couldn't withstand unrest and the onslaught of other peoples."
The researchers said the collapse of the Assyrian Empire is comparable with the current political situation in the Syria and northern Iraq. They also draw parallels with cities like San Diego and Los Angeles, where areas grow too large for their environments.
"The Assyrians can be 'excused' to some extent for focusing on short-term economic or political goals which increased their risk of being negatively impacted by climate change, given their technological capacity and their level of scientific understanding about how the natural world works," the authors wrote.
"We, however, have no such excuses, and we also possess the additional benefit of hindsight, which allows us to piece together from the past what can go wrong if we choose not to enact policies that promote longer-term sustainability."