Bad weather may have driven the mighty Mongols from Hungary. The Mongols' retreat shows that small climate changes can influence historical events, researchers argue May 26 in Scientific Reports.
In the early 1200s, the Mongol empire had expanded across Eurasia into Russia and Eastern Europe. But when the Mongols got to Hungary in 1241, they invaded and then suddenly retreated back to Russia in 1242. Though theories abound, historians have never found a clear reason for the abrupt exit.
Now, Ulf Büntgen of the Swiss Federal Research Institute in Birmensdorf and Nicola Di Cosmo of the Institute for Advanced Study in Princeton, N.J., think they may have an explanation. Weather data preserved in tree rings points to a series of warm, dry summers in the region until 1242, when temperatures dropped and rainfall increased. The shift to a wet, cold climate caused flooding and created marshy terrain. That would have been less than ideal for the nomadic Mongol cavalry, reducing their mobility and pastureland.