The sudden withdrawal of the Mongol armies from Hungary in 1242 may have been influenced by environmental factors according to a new study in Scientific Reports.

The Mongols began their expansion in the early 13th century and by 1279 had conquered much of Eurasia including China, central Asia, Russia and Iran. In early 1242 the Mongols crossed the Danube into western Hungary and, after a further two months, suddenly began to withdraw via a southern route through Serbia and Bulgaria, back to Russia. No reason is given in Mongol sources to explain their departure.

Using tree-ring data and documentary sources that include information on weather fluctuations and climate, Ulf Buntgen and Nicola Di Cosmo investigated environmental conditions between 1230 and 1250. The authors suggest that the climatic conditions that occurred in Hungary between 1241 and 1242 had an impact on the productivity of the land as well as on the suitability of the terrain for military operations of the types performed by Mongols. They argue that small climatic fluctuations resulted in marshy terrain across the Hungarian plain, which led to reduced pastureland and decreased mobility, as well as hampering the military effectiveness of the Mongol cavalry. The climatic changes from 1241-1242 may have been sufficiently extensive to alter the conditions under which the Mongols first invaded Hungary and thus could have contributed to their withdrawal.