At http://phys.org/print383558171.html … in 1242 the Mongol army was set to conquer central Europe when it mysteriously turned around and went back into Russia. A new study claims it was climate that persuaded the Mongols to put the conquest on hold, although the normal interpretation is that internal Mongolian politics were involved. They never attempted to subdue central and western Europe again. Now, climate change is blamed for a lot of things and at this point in time we are talking about temperatures getting much colder (rather than warmer). Mongol horses were brought up on the steppe and were used to steppe conditions for their nutrition – grasses and herbs. The herbs are an important part of the diet of horses and there may lie a clue. The winter of 1243/2 was very cold and frost lingered late. The Mongols appear to have opted for a spring offensive – but the thaw had set in and it was not only muddy but flooding was a problem. Could a massive army be thwarted by water?
Having said that the 1240s were a peculiar period. Matthew Paris, a monk at St Albans Abbey, wrote a chronicle and the 1240s and 1250s included lots of unusual natural events, even a plague that struck French troops (see www.warfare.altervista.org/13/Chronica_Majora-French_Troops_Dying_of_Pla… ) so we can be sure that there was more than just water involved – possibly bad omens of some kind.