Maya

The Maya star in Mel Gibson's classic movie Apocalypto.

...

... okay, FINE.

The Maya are the Yucatec branch of a larger ethnolinguistic group along the Gulf of Mexico and especially that big bulge including the Yucatan peninsula, in Mesoamerica. That group has been labeled "Maya" because the Yucatec were the first Maya whom the Spaniards met when they came over, and that is what those "Maya" called themselves. There survive other Maya branches: like the Huastec spinoff up the coast, the Quiche who wrote the Popol Vuh, and - most of all - the Cholti, whose language recorded what we know as "Classic Maya" civilisation.

Although the Cholti and, later, the Yucatec owned the only truly literate script in the New World - a hieroglyphic rebus, like the Egyptians' - this script was "forgotten". By which we mean, the Spaniards systematically suppressed it. Bishop Landa was the worst culprit but, ironically, he was also the man who did the most to transmit the script to us: he scribbled down its most-significant ideograms, and also encouraged the locals to write down their works into Latin script.

As (partially) a result, the Maya languages survived to the present day and are in better shape than are most Mesoamerican languages. Also, Michael Coe and Tatiana Proskourieff were able to pick up on what Landa started, and deciphered the old script. Despite Eric Thompson's best efforts.

So: what did Coe and Проскуряко́ва find? weellll... the Maya were assholes. Er, sorry. But they did a lot of city-on-city warfare and mass murders, and human sacrifice, and slavery. I guess you could say that everyone was doing it in that time and place, and the Spaniards weren't much better (although better than the Portuguese at least on the slavery thing).

They also used heavy metals in their paints, which dribbled into the water supply, and that cannot have helped. Their agriculture was a little more sustainable until it, you know, wasn't. At the end, the Chorti commoners mostly said fuck-this-noise and went back into the forests.

Currently Copan still speaks Chorti, and there are some other communities out west speaking related Chontal, but mostly other Maya peoples carried on that civilisational torch. Mostly the Yucatec.