In its earliest ages of civilization, Onderon was a world marked with savage jungles that were filled with dangerous creatures. To survive, the primitive human inhabitants of the planet protected themselves behind the walls of fortified settlements. Over time, these grew to become enormous walled cities, like the planet's capital, Iziz. Onderonian society developed so that criminals were outcast into the wilds, but the most resourceful of the exiles were able to tame the jungle's beasts and survive.
In the modern era, during the time of the Clone Wars, the planet's monarch King Sanjay Rash allied Onderon to the Confederacy of Independent Systems. Many Onderonians, however, refused to recognize the legitimacy of Sanjay's rule -- they preferred the neutral stance championed by former monarch Ramsis Dendup, whom Rash ousted. These dissidents banded together to launch an insurgency against the throne of Iziz, unsettling the planet. The Republic saw an opportunity to take advantage of this discord and manipulate the conflict in the hopes of freeing Onderon from Separatist influence.