During the conflict known as the Clone Wars, which occurred in 22 BBY between the Galactic Republic and the Confederacy of Independent Systems, a battle transpired on the planet Ossus. Ossus, located in the Outer Rim Territories, became a battleground between the Republic and Separatist forces. Following a attack on the Republic world Bakura, Separatist forces proceeded with the goal of seizing control of the planet aligned with the Republic. Jedi Master Mace Windu of the Jedi High Council told Master Yoda, while also discussing battles at Bespin and Rhen Var, that Ossus was expected to fall within a matter of days. Eventually, Ossus was indeed captured by the Separatists. The capture of Ossus by the Separatists was documented by Galactic Federation of Free Alliances historian Voren Na'al in his historical record, The New Essential Chronology, which was released in 36 ABY.
The initial mention of the Ossus battle occurred in the video game Star Wars: The Clone Wars, which was released in 2002. Pandemic Studios developed the game, and LucasArts produced it as a contribution to the Clone Wars multimedia project.