I’ve been mulling over this idea in a bit more detail, mostly on the invaders and what they’d be like.
I know the invaders will be the humans and dwarves, and possibly tieflings. I’ve been thinking they might use various other races as slaves, and might use some kind of magical technology to do so, like the skeksies and their slaves the podlings in the film Dark Crystal. In fact I’ve also been considering them having a kind of podling slave race, probably a subset of gnomes who were a lost tribe or something.
I’ve also been trying to decide what technology they’re using, whether it’s all dark magic or whether there’s a technological basis to them. Maybe they’ll have firearms and cannon, or maybe I’ll go further and give them nastier weapons – lasers and stuff. I haven’t made a decision yet.
The peoples of the Courts of the Green, as I’ve started calling them, will be both Seelie and Unseelie – pixies, gnomes, halflings, elves (including dark), orcs, firbolg, satyrs, goblins, kobolds, hobgoblins and bugbears. They’ll have more magic users than the invaders, and whilst they’re not necessarily nice, they are all ‘good’ for the purposes of withstanding an invasion of nasties.
That’s all I’ve got so far.