Faerun.

[rdonj]

I don't really have that much in depth knowledge about faerun (I have a copy of baldur's gate 2... that's about it), but my first instinct would be to go either political or factional. Perhaps both actually. Deity based doesn't really make sense and would probably never work.

Remember that most of the inhabitants of the world are human, and while there are differences between them I don't there would be a huge difference in the kind of troops available for the most part. You could probably come up with a fairly generic mega-roster and give some of the units to some nations and not others. For non-humans it would probably be a bit more work, but I think you should probably avoid these at least for a little while if you are going to do it. I would also highly advise you NOT try to make all ages, that would take far too much work and I'm not sure how sensible you could make it. Doing it all in LA makes sense to me.

I would consider making some of the stronger factional units into summons, probably as national spells for the nations that get access to the particular factions.