The Fire Nation took over the world, but they were long ago replaced by a semi-democratic government when the last of the royal family with bending died off. The rest of the family faded into obscurity.
The wars killed off most of the world, so the population of the planet is way less than modern earth but still more than in the canon 'verse. (In other words, there are still large swathes of land that are wild and unoccupied). The animals are still Avatar-verse hybrids, but the technology is much the same as on present-day Earth.
As of 04-23-12, I have posted all that I intend to for this fic. It was an interesting experiment, and I got over 40,000 words out of it (most of which are posted here- some bits weren't good enough to bother with). The story isn't complete, but I feel like it ends on a good note here. The rest of what I had planned parallels canon closely enough that I didn't want to bother writing it.
( TIMELINE )