The Shadows Cast
All the history that we have from the Green Era is from the Wood Elves or the documents that have been discovered in the ruins. Since it's not all that reliable, and it makes you want if you hear about it, I'm gonna tell you the bare minimum to get yourself around alive. You need to know this crap because otherwise you'll walk into Kanra boasting about some shit you did in Feuls and get yourself killed.
The Green Era spanned Driea before the world collapsed – I'll get to that – and is aptly named. It was a time where life flourished, magic was commonplace, and you didn't die if you drank the rainwater; many of the remaining Wood Elves have described it as paradise. and because anything that is described as paradise has to be destroyed apparently, Demons decided to end the Green Era. Yeah, yeah, you can tell me that demons and gods don't exist and all that bullcrap but I'm the one who did the research so you can fuck off. Anyway, the demons contacted anyone who would listen – cults, warlocks, paladins, clerics, anyone – and told them of man's corruption, and how to stop it. Sadly that included a lot of dark magic, a little bit of science, and a whole lot of burning to death. I can tell you whatever they did worked, since we have a red sun and both gods and demons have said fuck you and grown silent.
As the name suggest, and what you know from the fact that you live in it, this is what happened to the world after all the world ending bullcrap earlier.