Onderon
The native Onderonians struggled against the beasts, eventually gathering new technologies and building the huge walled city (and only city on Onderon) of Iziz to protect themselves from the beasts. Later, the Onderonians began to send their criminal element out into the wilderness without any protection from the beasts. These outcasts soon learned to defend themselves, and eventually formed a second civilization. Relations between the two groups were hostile, and they remained at war with each other for many years.
Onderon was also the planet on which the Sith Freedon Nadd attempted to found a new Sith Empire. As a matter of fact, he founded the Onderon royal line and his tomb is located on the jungle moon of Dxun.
Eventually the Old Republic asked the Jedi to watch over the world. The Jedi Master Arca Jeth took over as watchman and assigned his padawan Ulic Qel-Droma to the planet. The war was finally ended when the Onderonian princess Galia married the Beastprince — although tensions remained for long after that.
[edit] The Mandalorian War
During the Mandalorian War, Dxun and Onderon were among the first planets to be invaded by the ruthless Mandalorians. However, the Republic intervened, and the remnants of the Mandalorians were forced off Onderon.
However, not all the citizens were enthusiastic about Onderon becoming part of the Republic. Those who remained loyal to the Republic gathered around the young and weak Queen Talia, and those who thought the Republic brought nothing but problems supported her cousin, General Vaklu, who often argued with her and didn't hide the fact that he wanted to be crowned king. Not many of his followers, however, realized his true intentions.
[edit] The Civil War
In the cataclysmic aftermath of the Jedi Civil War, Canderous Ordo, proclaimed the new Mandalore, reunited some of the scattered Mandalorian clans at their former base on Dxun. When the Jedi Exile, in his search for Master Kavar, crash-landed in the jungles of Dxun, Mandalore offered his shuttle to sneak through the military blockade of Onderon — something the Ebon Hawk could not accomplish.
From the city of Iziz, the Exile and Mandalore managed to contact Master Kavar, who was an advisor of Queen Talia, but were forced by Vaklu's troops to retreat to Dxun. Shortly after, the Iziz starport was closed, and the civil war between Vaklu and Talia began.
The Exile left the Onderon system to find other hidden Jedi Masters. When his quest was finished, the droid T3-M4 received a message from Kavar, asking for help against Vaklu.
Upon return to the Mandalorian settlement, the Exile discovered that Valku received a not-so-unexpected assistance from the Sith Order, which intended to make Onderon one of their military bases should the Republic lose control of the planet.
The Exile had to separate his forces. He dispatched three of the Ebon Hawk crew to infiltrate the Sith base on Dxun, and, together with Kreia and another companion, set off to Iziz onboard a Basilisk war droid, a Mandalorian vessel barely large enough for three people. With their aid, as well as the aid of Master Kavar, the royalists managed to break through Vaklu's blockade to the Queen's palace, arriving to see the two leaders clash their swords in the throne room.
Queen Talia orders her soldiers to shoot Vaklu immediately, thinking that he will be able to break out of any prison. However, the Exile stops the execution and tells Talia that executing Vaklu will only make him a martyr, and that the queen should use this time to rebuild her planet and re-earn her people's trust. Talia calls off the execution and allows Vaklu to stand trial fairly. The Exile earned the Queen and the Jedi Master's respect for keeping Onderon within the Republic. Later, Kreia predicted that Talia would rule for a long time, bringing peace and happiness to her beloved people. The Onderonians themselves would eventually drop their traditions and culture and become subsumed within the greater Republic.
Jedi Master Kavar is later killed by Kreia while attempting to strip the Exile of the ability to feel the force.