"We only need a superficial grasp of history to appreciate that it is essentially complex, chaotic and totally unpredictable. European history for example would have been very different if the Mongols had not turned back after they had reached the borders of Austria in the early years of the 13th century. Some historians have suggested that was the result of stiff Hungarian resistance, but others have offered a much simpler and far more prosaic explanation: in the spring of 1242 the great Ogedei Khan died at the age of 56 after a late-night drinking bout. News of this soon reached Batu Khan, who was one of the contenders for the throne, and he immediately returned to stake his claim and in so doing he gave up any attempt to extend the Mongol empire any further West." -- Rob James, Christian Today.
Alternative View: The Mongols Never Really Had A Chance to Take Europe.