That is an insane statement about Mali - "second largest (after the Mongols)."
As was already discussed in this thread, it's misphrased, not insane.
The Mali were, at the time of their greatest extent, the second largest empire in existence at that time, after the aforesaid Mongols. China at its peak wouold have been greater, but during Mali's peak, it was Mongol. Idem Russia. England at its peak or Spain at its peak would be greater, but one didn't even exist, and the other was a small island at the time Mali was as its Zenith.
They were relatively insignificant to the affairs of world history. Not humanity, world history.
And yet their gold fueled the European renaissance, and one of the motivation for the Portuguese to explore down the coast of Africa was to find an alternate route to the wealth of Sub-Saharan Africa than the Mali/Songhai controlled Trans-Saharan trade routes.
As far as criticism about the Aztecs being an empire, they absolutely were. Check out their history - they militarily conquered all of MesoAmerica
The Tlaxcallans, the Tarascans, the Zapotecs, the Mixtecs and a wide variety of assorted Mayan City-States would like a word with you, if you please...
More to the point, the Aztecs controlled a part of the northern half of Meso America, which is itself a fairly small region (essentially, southern Mexico) of North America.
and made slave runs to honor their gods, and as far as I can tell, for fun.
No, they waged localized wars with their neighbors and sacrificed some of the captured warriors, in order to keep the sun and the world from dying out on them. One presume that continued existence is a matter of more than just fun.
That makes for a powerful empire.
What, holding human sacrifices in a territory that's about a third or a quarter of Mexico?
Maya was not a full-fledged empire, they were a trading, and warring, collection of city-states much like ancient Greece - pre-Alexander.
Mostly true, although there were several occasions where one of the city States essentially came to dominate the others until the next revolt. Mayapan comes to mind.
Incans, like the Hittites, was a powerful kingdom, dominated by their central city, but not an empire.
...I'm confused. What did the Aztecs do that the Incans didn't that you'd call the Aztecs an empire and not the Incans?