It's roughly 2,000 kilometers from St. Louis to modern Mexico city, as the crow flies; a little farther to the Yucatan. The Mississippi river and the Gulf of Mexico provide reasonably direct water links. Is there any evidence that trade, diplomacy, or other communication occurred between Cahokia and either Aztec Empire or any of the Mayan kingdoms?

Certainly some ideas defused, most obviously the key crops of corn, beans, and squash. To my untrained eye, Mississippian artwork resembles Mesoamerican, but that's not diagnostic.