4.2-Kiloyear Event

The 4.2-kiloyear event was a severe aridification episode, a long term megadrought, that began around 2200 BC and ranks among the most significant climate disruptions of the Holocene epoch. Researchers have proposed that it triggered the collapse of Egypt's Old Kingdom, the Akkadian Empire in Mesopotamia and the Liangzhu culture of the lower Yangtze, and some link it to the decline of the Indus Valley Civilization and to Indo-European migrations into India, though other scientists dispute the finding, arguing the evidence does not show a clear global drought on a consistent timeline.