Avatar the last airbender

These days, I am kind of attracted by an animated cartoon. This animated cartoon was produced by America, but the story was from East countries. It mentioned four important elements of the world: Water, Earth, Fire and Air. These four elements can keep the world in balance.
Background:
In a lost age, the world is divided into four nations: Water Tribes, Earth Kingdom, Fire Nation, and Air Nomads. Within each nation, there is a remarkable order of men and women called the "benders" who can learn to harness their inborn talent and manipulate their native element. Bending is a powerful form combining martial art and elemental magic.
In each generation, only one bender is solely capable of controlling all four elements. That bender is the Avatar. The Avatar is the spirit of the world manifests in human form. When the Avatar dies, it reincarnates into the next nation in the cycle. Starting with the mastery of his or her native element, the Avatar learns to bend all four elements. Throughout the ages, the countless incarnations of the Avatar have served to keep the four nations in harmony.

This story is more like Chinese mythology. The leading characters' name are Aang-the avatar, Katara and Sokka---sister and brother from the Water Tribes. The four nations were living in peace before the Fire nation started attacking. Only the avatar could master the four elements of the world and only he could stop the Fire nations' attack. But when the world needed the Avatar the most, he disappeared. After a hundred years, Katara and Sokka discovered Aang in a huge ice hill, and then they helped Aang to find a way to stop the Fire nation's attack...