I have a great conflict for the ending of the series. After Aang defeats the Fire Lord, restores balence to the world, and frees the world of the evil of the Fire Lord, after that happens, the Earth Kingdom generals, want to conquer the Fire Nation for themselfs, and give the Fire Nation a taste of their own medicine.
Aang and his friends think that is wrong, and would be sinking to the Fire Lord's level, and they already got the bad guys, and all they would be doing is punishing the citizens of the Fire Nation for stuff the Fire Lord and the Fire Nation army did. And in a reversal?? of things, the Avatar has to protect the Fire Nation from the Earth Kingdom army.