A few dozen Spanish with muskets and swords defeated 5 0r 20 million Aztecs, so yeah, the Marines would win, unless they ran out of bullets.
Common misconception. Conquistadors had hundreds of thousands of South American tribesmen as allies because the Aztecs had been slaughtering the neighboring tribes for centuries. Neighbors wanted seriousnpayback. Kinda ruins the libs portrayal of Pre-Columbus Americas as nirvana.
Not exactly. The Aztec client states rebelled and attacked along with the Spanish in an attempt to throw off the Aztec oppression. And there were a lot more of them then there were of the Aztecs.
Of course, later they found out the Spanish were not much better. That is usually the way it goes.
their primary weapon was smallpox.
The Spaniards that defeated Montezuma existed at a transitional period of warfare. Muscle powered weapons were slowly giving way to fire-fighting. The Spaniards could continue to fight even when their powder & shot were expended as fire-fighting was a “fair-weather” activity in those days.
Then you have the fact that the Aztecs never saw warhorses or war dogs. Both would have been as terrifying as an Abrams or an LAV, and neither of the latter can live of the land.
Finally we know that the Spainiards made use of native allies. This was the key to their victory. The Marine MEU would have to do the same. I think that would be most difficult as that is a SpecOps function and the Italian city-states mostly remained loyal to Rome during Hannibal’s depredations.