That is the conclusion of a study recently published in the Proceedings of the National Academy of Science. The researchers used tree ring data to determine that, following an extended period of drought that likely caused social and political upheaval, an unprecedented period of persistent rainfall led to bumper crop of grass and hay across the Eurasian steppe. The upheaval created the political conditions that enabled Genghis Khan’s rise to power, and the flowering of the steppe provided the fuel for his mounted armies and their conquests.
I am still considering how this fits into classical geopolitical theories – particularly Mackinder and Spykman, who were so influenced by the historical repetition of Central Asian armies of conquest. It is compelling evidence, however, for profound short term political impact of climactic events, even on a decade-level scale.