In 1241, the Mongol army marched into Hungary, defeating the
Polish and Hungarian armies and forcing the Hungarian king to flee.
In 1242, despite meeting no significant military resistance, the
Mongols abruptly packed up and hurriedly left. This historical
mystery has never been solved. Until now.
A visitor joked : "This story wasn't in the bible, so it
can't be true. Anyone who believes this is going to hell."
https://sg.news.yahoo.com/mystery-mongol-retreat-hungary-solved-132919172.html
Due to climatic and landscape conditions