Climate may have defeated Mongol invaders

Climate fluctuation not only may have paved the way for Genghis Khan’s conquests of Asia in the 13th century, sudden climatic change may also have halted the Mongol invasion of Europe, according to new research.

Two scholars − one skilled in historical documents and another in interpreting tree rings to deliver weather reports through history − say that cold and heavy snowfalls may have blighted the pastureland of the Great Hungarian Plain in 1242.

This would have produced marshy conditions that would have made it difficult or impossible for 130,000 horsemen to campaign or even survive so far from home.

Genghis Khan’s vast but fleeting empire began in 1206, when the leader united the Mongol tribes, and by 1279 one hitherto impoverished group of nomads had swept across China, Russia, central Asia and Iran. Genghis died in 1227, but by 1242 an army of 130,000 Mongol cavalry had entered Hungary.

On the march

In 2014, a team of US scientists looked at tree ring and other data and found that the explosion of Mongol power from a harsh, dry homeland coincided with a mild climate spell that must have produced good pasture that was ideal for nomads on the march. So conditions made military adventure possible, they hypothesised.

Now Ulf Büntgen, a dendrochronologist at the Swiss Federal Institute for Forest, Snow and Landscape Research, and Nicola Di Cosmo, a historian at the Institute for Advanced Study at Princeton in the US, think that another change in the weather may have saved Europe from the Mongols.

They suggest in the Scientific Reports journal that local climate change may have been behind the sudden and unexplained decision of the Mongol army to withdraw to Russia.

Their study is just the latest in a long list of papers that link social turmoil and collapse of imperial power with changes in climate. Dr Büntgen himself was one of a team that recently linked the turmoil of Europe’s so-called Dark Ages with a Little Ice Age between 556 and 660 AD.

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Such arguments are necessarily tentative: history is complex and records unreliable. But the tree ring chronologies from the period tell a story of cold, wet conditions in early 1242, when the seemingly-invincible Mongols crossed the Danube into western Hungary.

But after two months they withdrew, through Serbia and Bulgaria. And although historians have been conjecturing reasons for the retreat for the last 700 years, the Mongol generals left no record or explanation of the decision to leave Hungary alone.

So climate scientists took up the challenge. “Marshy terrain across the Hungarian plain most likely reduced pastureland and decreased mobility, as well as the military effectiveness of the Mongol cavalry, while despoliation and depopulation ostensibly contributed to widespread famine,” the researchers write.

“These circumstances arguably contributed to the determination of the Mongols to abandon Hungary and return to Russia.”

Initial victories

Geography certainly played a part in the Mongol advance. A great stretch of open grassland or steppe links the Mongolian homeland with the Hungarian plain, and the invaders entered Europe through the Carpathians to win convincing initial victories.

Hungary’s King Bela IV fled to Austria and the Mongol cavalry pursued him to the Dalmatian coast, and seemed to prepare for a long campaign. And then, abruptly, the Mongols departed. Some believe it may have been because of the death of the Great Khan’s successor in 1241; others believe that the Mongols were really pursuing another set of nomads, the Cumans.

But medieval armies provided for themselves only by forage and pillage, and there is also evidence that, given the climate conditions, the grasslands of Hungary could not have provided for so vast an army.

This is not the kind of debate that could ever be satisfactorily concluded, but authors of the Scientific Reports study are content that climate aspects may have played a part and contributed to withdrawal.

“Our ‘environmental hypothesis’ demonstrates the importance of minor climatic fluctuations on major historical events,” they write.