In a lost age the world is divided into four equal powers:
Water Tribe,Earth Kingdom, Fire Nation, and Air Nomads.
In each nation there's a group of gifted people known as Benders who have the ability to manipulate there native element using martial arts and elemental magic.
For thousands of years the nations lived together peacefully. But then disaster struck.
The young ruler of the Fire Nation, Fire Lord Sozin, began a war of world conquest.
The only one who could have prevented it was the Avatar. The Avatar is the human incarnation of the Spirit of the World, he alone can master bending all four elements.
But, just when he was needed most, he disappeared.