"then inexplicably vanished, leaving no trace behind in the historical records."
No trace, because the winners write the history books -- if they know what they're doing, that is.
I remember reading some works of Confucius. He always talked about southern kingdom where people painted their body, wore not much clothes or wore some strange decorations.
That is probably how those from the North viewed the southerners, half naked barbarians wearing funny or weird stuffs. It almost gave the impression that he was describing tribal primitives. However, it is possible he was putting them down.
Yes, but. Records are records. Civilizations have ended and left records. I wonder if we will leave records. Those plastic pieces we carry around are probably indesructable, but the data they carry may decay over time. There are billions of PCs and many would survive even a massive asteroid impact, but what about the CDs? In a thousand years would our record be nothing but a collection of Doom3 and Dune2000 games?