The "aztecs" (Mexica) are not a good example. The Fall of Tenochtitlan was facilitated by an alliance between the Spanish Empire and Tlaxcala.

The Tahuantinsuyu (Inca) had a civil war of succession followed by a purge of the nobility after the monarch died Huayna Capac of smallpox.

So not even in those cases they faced a unified front.

And the innovations you mention are not enough. On one side you have no navigation technology (map making, compass, etc), no animal traction.