askchapo

Entire thing is incredibly suspicious. Their civilization lasted for at least 65 million years. 65 MILLION years, meaning it was incredibly static and they didn't fallen at any point in this time. And we know they didn't until 20-something millenium because there was apparently peace with humanity, full power Eldar empire could destroy humanity at any time, but they instead allowed humans to take nearly entire galaxy (with their empire being fairly small territorially, most of their population concentrated in what later became Eye of Terror). Now can you imagine what would happen if entire Eldar empire was like drukhari? They would slaughter or enslave humanity, which didn't happen. Conclusion is that they weren't decadent as a species.

Incidentally, their fall happened roughly at the same time Emperor started to seek to lead the humanity. But what prevented him? Humanity being too powerful, Dark Age human empires would't accepted his rule easy, and Eldar with their incredibly powerful psykers posed a mortal threat too.

My theory is that being crazy deranged nazi (and most powerful psyker in galaxy) he caused the fall of Eldar, possibly using small decadent faction (remember that the main source on decadency of Eldar is Vect words and he's not really famous for truthfulness and he also have every reason to portray every Eldar as being as fucked up as he is) thus starting the turmoil that would eventually turn into Age of Strife and prepare the galaxy for his conquest.