<P> Rashid Al - Din, a historian of the Mongol Ilkhanate, explicitly states in the Ilkhanate's official histories that the Mongols were not even aware of Ogedei's death when they began their withdrawal . Rashid Al - Din, writing under the auspices of the Mongol Empire, had access to the official Mongol chronicle when compiling his history (Altan Debter). John Andrew Boyle asserts, based on the orthography, that Rashid Al - Din's account of the withdrawal from central Europe was taken verbatim from Mongolian records . </P> <P> Another theory is that 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 local climate shifted to a wetter and colder environment . That, in turn, caused flooding of the formerly dry grasslands and created a marshy terrain . Those conditions would have been less than ideal for the nomadic Mongol cavalry and their encampments, reducing their mobility and pastureland, curtailing their invasion into Europe west of the Hungarian plain, and hastening their retreat . </P> <P> The true reasons for the Mongol withdrawal are not fully known, but numerous plausible explanations exist . The Mongol invasion had bogged down into a series of costly and frustrating sieges, where they gained little loot and ran into stiff resistance . They had lost a large number of men despite their victories (see above). Finally, they were stretched thin in the European theater, and were experiencing a rebellion by the Cumans in what is now southern Russia, and the Caucasus (Batu returned to put it down, and spent roughly a year doing so). Other argue Europe's bad weather had an effect: Hungary has a high water table so it floods easily . An analysis of tree rings there found that Hungary had a cold wet winter in early 1242, which likely turned Hungary's central plain into a huge swamp; so, lacking pastures for their horses, the Mongols would have had to fall back to Russia in search of better grasslands . </P> <P> Regardless of their reasons, the Mongols had completely withdrawn from Central Europe by mid-1242, though they still launched military operations in the west at this time, most notably the 1241--1243 Mongol invasion of Anatolia . In fact, Batu specifically decided against attending the kurultai in favor of staying in Europe, which delayed the ceremony for several years . </P>

Unlike much of the rest of western europe in the 13th century