White settlers drove the advanced Cahokia civilization from the major city they built for themselves and then made up a bunch of nonsense about other ancient people building the city to justify the ethnic cleansing! Truly awful. What year did this all go down, Wikipedia?

The population of Cahokia began to decline during the thirteenth century, and the site was eventually abandoned around 1300[18] The area around it was not reoccupied by indigenous tribes[19] to 1350.[20] Scholars have proposed environmental factors, such as over-hunting, deforestation, and flooding, as explanations for abandonment of the site.[18]

Another possible cause is invasion by outside peoples, though the only evidence of warfare found so far are the defensive wooden stockade and watchtowers that enclosed Cahokia's main ceremonial precinct. Due to the lack of other evidence for warfare, the palisade may have been more for ritual or formal separation than for military purposes. Diseases transmitted among the large, dense urban population are another possible cause of decline. Many theories since the late 20th century propose conquest-induced political collapse as the primary reason for Cahokia's abandonment.[21]

Ahh, it was those white settlers in the year 1300.

[1] https://en.wikipedia.org/wiki/Cahokia