User blog comment:Spartian300/alternative history: Middle ages invaded./@comment-1789156-20131219024348/@comment-32656-20131231142558

The size of the Mongolian empire is also exaggerated - most of it was devoid of people and empty.

Doesn't matter how many rulers you base it off of. One ruler-based, and it falls rapidly. If more than one, it has to be a slow progression, and in populated areas... and that will not only take forever, but will not last.

Fact of the matter is, it is impossible for a state at that technological level to have an empire larger than Rome or China. Let alone planetary or near-planetary.

And, something you miss: The Mongolian Empire was after the era you talk about, too.