So, Mesoamerica was apparantly very populated before the Spanish came along. The Tarascans, a rival state of the Aztecs, managed to raise 100,000 warriors when a party of Spanish came along and the Aztecs had around 300,000 themselves.
So, what if the smallpox and other diseases hadn't eradicated most of the Mesoamericans? You might say that it'd be impossible for the Spanish to control such a large population, but this is a what if scenario that's about Spain controlling Mesoamerica, despite everything, even if it's impossible for them to do so, even if it wasn't very clear in the title. What kind of effect would it have on Spain to have full control of a fully populated, rich land like pre-Spanish Mesoamerica?
Also, some off topic questions:
Why were the Mesoamericans and other isolated peoples susceptible to European diseases but not the people of Subsaharan Africa? Besides some contact at the coast, I thought there were never any contact between Europeans/Arabs and Subsaharan Africans.
Also, could you compare pre-Spanish Mesoamerica to say, Greece, when it was still in its city-state form? The Aztec Empire reminds me of the Delian League and there were lots of city states in Mesoamerica apparantly.