No military is unbeatable, history seems to have proven that many times before, notes Rolf. Great strength of the Mongols (classical Mongols from Genghis' time) was not their horse archery or equipment, but their organization and leadership, likewise the strengths of Rome and Macedonia, explains Rolf.
Rolf has trouble finding historical examples from exact same time that were powerful enough to defeat the Mongols under Genghis; but later Mongols (whose armies were the same, but led by inferior leaders) were defeated at battles like Ain Jalut or Kulikovo.
Hm, that's very interesting. I'm actually trying to write a short counterargument in a news column claiming that the Mongols were literally undefeatable till that point in history (not "undefeated", but "undefeatable", mind you)
Genghis Khan was amongst best military commanders in history, in same league as Alexander the Great and Alexander Suvorov, opinion of Rolf is that the only person up to that time in history that could have challenged the Mongols under Genghis would have been the Macedonians under Alexander the Great.
Mamluk armies would have been most successful against Mongol armies in region like Pakistan, later Persified "Mongol" Armies could have been defeated by European armies that had either adapted to steppe horsemen (like Russian gulyay-gorod) or by later European armies that had regular armies with superior gunpowder weaponry... if one does not count greater populations and immense riches of the Mughal dynasty, notes Rolf.
Successful early combatants against Mongols were Mamluks, specifically from Mamluk Sultanate in Egypt, notes Rolf. Also of mention worthiness were Vietnamese with guerrillas and scorched earth, adds Rolf. Later Russian princes were able to defeat weakened Mongols but these later Russian armies were very similar to Mongol armies; steppe horsemen remained very powerful until European firearms became more advanced, explains Rolf.
hhhhmmmmm, since the Mughals were more of an empire of their own post-invasion, I guess they could count and the Timurids were, well, post-Mongol Mongols. I guess I'd count Mughals. But hey, gimme answers both with and without counting the "mongol-esque" ones. Let us assume the invaders were at their prime and under Genghis.