So, just finished reading the Comanche Empire. A fascinating look at how the Comanches evolved and changed as they adopted horses, and how they would demand tribute or raid the Spanish colonies in New Mexico and Texas.
The author doesn't make the comparison, but there seem to be a lot of similarities between the Comanches and nomadic empires in Eurasia. They were bought off with tribute--- sorry, gifts, which the Spaniards and Mexicans hoped would civilize them; if their ...demands were not met, they would raid their neighbors. It's interesting because they seemed to have reached their apogee in the 1830s and 1840s, raiding south into Mexico, and briefly reaching only a couple hundred miles north of Mexico City. meanwhile, their society underwent rapid social stratification with an underclass of slaves they captured from New Spain/Mexico and neighboring tribes.
And then their population collapses due to overexploitation of the buffalo, disease, and the US army. Sic Semper Nomadis.
Anyway, a couple of thoughts: 1) In a world with European expansion, could we see nomadic empires in the Plains raiding southward, eventually overrunning Mesoamerica? and 2) what about an actual Comanche Empire? They never really set up an administrative system, content to raid, demand tribute, and trade, but an 18th century Comanche Genghis during the Mexican War of Independence would be pretty interesting.