Water Tribe Civil War

The Water Tribe Civil War is a conflict between the two Water Tribes.

Prelude
In 151 ASC, in the Northern Water Tribe, Unalaq, the the spiritual second son of the then-Tribe Chief, wanted to usurp the throne from the heir-apparent, his older brother, General Tonraq. Exploiting his brother's lack of spirituality and, Unalaq framed Tonraq by hiring a band of barbarians to attack the Northern Water Tribe. Tonraq managed to ward the mercenaries out of the tribe. Unalaq instructed the barbarians to hide in the nearby spirit forest, knowing Tonraq will ferociously go after them. Tonraq indeed followed the barbarians in the forest and apprehended them, but in the process, the forest was destroyed.

Destroying the forest angered the dark spirits, and attacked the main city. Tonraq tried his best to battle the spirits using combative waterbending, but Unalaq sprung into action, performing a highly-advanced waterbending technique to tame the spirits and guided them back to the forest.

Due to the proportion of the damage the spirits caused because of Tonraq's attack in the spirit forest, the chief banished his firstborn. With this plan a success, Unalaq became chief instead.

Starting a new life in the Southern Water Tribe, Tonraq and his wife Senna, bore a daughter, Korra, who was then identified as the Avatar. Upon learning that her niece is the Avatar, Unalaq volunteered to teach Korra the spiritual side of her duties, an offer his brother rejected numerous times.