Assyrian Empire collapsed due to climate change

Ancient Mesopotamia, the land between the Tigris and the Euphrates rivers, was the center of the Neo-Assyrian Empire. The ancient superpower was the largest empire of its time, lasting from 912 BC to 609 BC in what is now Iraq and Syria. At its height, the Assyrian state stretched from the Mediterranean and Egypt in the west to the Persian Gulf and western Iran in the east. Then a reversal of fortune, and the Neo-Assyrian Empire plummeted from its zenith (650 BC) to complete collapse within the span of a few decades. The reasons why were a mystery. Research shows that climate change was the double-edged sword that first helped the meteoric rise of the Neo-Assyrian Empire and then lead to its precipitous collapse.

Rainfall patterns over Mesopotamia were deduced from cave stalagmites. These are the cone-like structures from the cave floor. They grow slowly, as rainwater drips down from the cave ceiling.

Oxygen isotope ratios build a timeline of how conditions changed, but don't reveal the amount of time that elapsed between them. Stalagmites trap uranium. Over time, uranium decays into thorium at a predictable pace. Experts made high-precision uranium-thorium measurements. The Neo-Assyrian state expanded during a 200 year interval of anomalously wet climate. This was followed by serious droughts in the early-to-mid-seventh century BC. This period marked the swift collapse of the Neo-Assyrian Empire.

Repeated crop failures likely exacerbated political unrest in Assyria, crippled its economy and empowered adjacent rivals.