The Battle of Commenor took place during the Second Galactic Civil War.
The Galactic Alliance objective was to contain Commenorian forces, not to occupy the world.
During the battle, elements of the Galactic Alliance Third Fleet launched a cloaked asteroid at Commenor. Pilots Caregg Oldathan and Danen of Grayfeather Squadron investigated and discovered it.
Realizing they could not hope to prevent it from colliding with their world, they pursued the ships responsible for the attack, hoping to exact vengeance and prevent the tactic from being used again.
The atrocity committed in the battle resulted in the Commenorians releasing the affliceria bacterium on Coruscant which infected many civilians and military personnel.