The Beast Wars, alternatively known as the Beast Wars of Onderon, represented a regional struggle that spanned approximately 400 years, commencing with Freedon Nadd's arrival on the planet Onderon. Ultimately, this conflict played a role in igniting the Krath Holy Crusade, which was a component of the larger Great Sith War.
The unusual relationship between Onderon and its moon, Dxun, gave rise to the Beast Wars. The moon's orbit was such that the atmospheres of the two celestial bodies connected once annually. Over many centuries, the Drexls, predatory creatures that flew and were native to Dxun, adapted to use this "oxygen bridge" to migrate to Onderon and establish themselves there.
As a defense against the Drexls' aggressive nature, the Humans of Onderon constructed a large, fortified city, which would become Iziz, to ensure their safety. Around the same period, a Dark Jedi named Freedon Nadd landed on Onderon, where he ascended to the position of king and initiated a dynasty steeped in darkness among the Onderonian royal family. A decree was soon issued that all criminals within Iziz would be banished to Onderon's wilderness, where they were expected to be killed by the Dxun beasts. However, due to the strong influence of the dark side within the royal house at that time, many of these "criminals" were merely individuals who opposed the monarchy. As time passed, a significant number of these exiles learned to tame the beasts and became known as the Beast Riders. They then utilized these creatures to launch attacks on Iziz, marking the commencement of the Beast Wars of Onderon.
The year 4000 BBY saw the conflict escalate to unprecedented levels. The Force ghost of Freedon Nadd cautioned Onderon's ruler, Queen Amanoa, that engaging in war with the Beast Riders would lead to her downfall. Consequently, she sought assistance from the Jedi to bring an end to the Beast Wars. Jedi Master Arca Jeth was assigned as the watchman for the Onderon system. He dispatched his Padawans, Tott Doneeta, Ulic, and Cay Qel-Droma, to resolve the issue on Onderon. Upon their arrival in Queen Amanoa's throne room, a group of Beast Riders executed a bold raid on the city and abducted Amanoa's daughter, the Princess Galia. The Jedi ventured into the wildlands to rescue the Princess, and Tott successfully tamed a boma, which guided them to the fortress of Beast-Lord Modon Kira. Upon entering the fortress, the Jedi discovered a wedding feast in progress between Galia and Modon's son, Oron Kira.
Ulic's attempt to rescue the Princess was met with her declaration that she, in fact, desired to be married. Modon organized a peaceful banquet to facilitate discussion, during which the Kiras revealed to the Jedi that the Onderonian royal family was under the influence of the dark side of the Force and the spirit of Freedon Nadd. Galia, Oron, and the Jedi, having reached an agreement with Modon that he would initiate an attack should they fail, returned to Iziz to confer with Queen Amanoa.
Upon their arrival, Amanoa unleashed her dark side powers upon them, compelling them to retreat into a concealed passageway. Oron informed his father via comm that they had been unsuccessful. Consequently, Modon's extensive gathering of Beast Lords from across Onderon advanced towards Iziz, with the Jedi engaging Amanoa's royal guard in combat within the throne room. During the battle, one of the guards utilized a halberd to sever Cay's arm, which was subsequently replaced with an arm from an XT-6 droid.
Amanoa attempted to shift the course of the battle by employing the dark side, but her efforts were thwarted by the newly arrived Arca Jeth's Jedi battle meditation, which enabled the beast riders to gain an advantage. Iziz soon fell. The Jedi, Oron, and Galia descended into the deepest levels of Amanoa's palace, to the tomb of Freedon Nadd. Amanoa was instantly killed by the pure light side of the Force emanating from Jeth's body, ending the dark side's half-millennium dominance over Iziz. Galia and Oron Kira were wed, uniting the beast riders and Iziz.
The conflict came to an end late in the year 4000 BBY.
In an effort to eradicate the dark side's influence over Onderon, Arca Jeth ordered the removal of Freedon Nadd and Amanoa's coffins from Iziz and their re-interment on Dxun. However, despite the damage inflicted upon his body by his use of the dark side of the Force, King Ommin remained strong in The Force, and incited an uprising among the Naddists, those Onderonians who continued to adhere to Nadd's teachings. Although the revolt was eventually suppressed, Ommin managed to impart much of his dark side knowledge to two Empress Tetan nobles, Satal and Aleema Keto, who had journeyed to Onderon in search of Sith artifacts.
Following Ommin's defeat, the spirit of Freedon Nadd manifested before the Ketos and introduced them to the dark side of the Force. Subsequently, the two would lead the Krath secret society in initiating a coup within the Empress Teta system, ultimately leading to the Krath Holy Crusade.