Avatar: The Storm of Ashes is a fan-made part of the Avatar: The Last Airbender timeline. It is set one month after the final book three episode: Sosin's Comet: Avatar Aang. The World is at peace until new land is discovered.
The Storm Of Ashes
This is not just the name of the fan fic, but the name of a rebellion of Firebenders! They have a military that is different from the fire nation armies. They are also called Inferno Empire because an Emperor/Emperess rules like a dictator. There is also a branch that consists of waterbenders. They were enslaved to fight.