With a POD of 1190 or later, what peoples could unite or suddenly burst out and conquer Eurasia, or at least a large chunk of it as did the Mongols, other than the Mongols? I imagine a different steppe people would be the best candidate, but I'm interested to see what you all think. How would said people go about their conquest?
Oh, that's easy!
You take any people, better a bunch of closely related tribes speaking one language. These tribes better be disunited and fighting each other for a couple of centuries or so - the fieriest war of everybody against everybody - that would make them tougher than coffin nails, and their bursting out from obscurity to the world dominance would be more spectacular.
These tribes better be nomadic for obvious reasons as their nomadic horse-archers kind of warfare is necessary for world-conquering.
The place where these tribes live better be the worst shithole on the Earth - you must freeze your balls off in winter (-50 Celsius) and make your balls fried eggs in summer (+50 Celsius). Droughts, deserts, mountains. Darwin's natural selection and surviving of the fittest for a couple of thousand years would make these people genetically best suited for long campaigns across Eurasia.
Did I forget anything?
Oh, ye, these tribes must have been living in the sphere of influence or very close to some "world empire(s)" for a few hundred years at least - as the art of empire-building is necessary.
And as a final touch -
- you give these tribes a "Great Man" - the best charismatic visionary founding father, politician and general, the type of man which are born into this world once in the history of the humankind.
Voila!