Mongols.

[godofthunder9010]

Of course, Europe was sabotaging itself. The Pope and other kings of Europe were even encouraging the Mongols to attack, in order to wipe out their rivals for them. Europe was very stupid that way.

It also was not nearly the prize in wealth and status that the Middle East and China were. My opinion is, Batu proceeded further into Europe as an afterthought once he avenged himself of the Cumens. They were still quite strong after Batu returned to Russa, but whatever the reason might be, the Mongols didn't bother with Europe again.

European tactics were sophisticated enough at the time, but they were completely unprepared for the sorts of tricks that the Mongols had. I still can't think of a potential situation where they were advanced enough to stop the Mongols decisively. Also, if Vienna had fallen, how strong would Europe's resolve have been?

 

[Airborne]

Well, I beleive both Vegetius and SUn Tzu wrote about how strong a entraped foe can be.

 

[godofthunder9010]

Of course, we'll never know. Its ludicrous that Europe was still busily sabotaging each other all the way up to the point of the Mongols withdrawal. I wonder far it would have gone on before they woke up.