The Battle of Cerea was a large and decisive three-way battle in 11 ABY between the Infinite Empire of the Sith, the Galactic Federation, and Cail's Empire. The battle was the climactic yet disappointing end of warlord Balmus Cail's otherwise strategically and tactically brilliant Semagi Campaign, his attempt to cut Federation control of the Spar Trade Route and Great Gran Run and endanger the enemy's attempts to reinforce their own systems in the region and mount offensives. As Federation forces began to falter, a massive Sith invasion fleet, led by Darth Ominus himself, came out of hyperspace and attacked both Imperial and Federation forces. Though they had successfully attacked under the element of surprise, Sith forces still suffered numerous casualties. The remainder of the Federation fleet jumped out of the system, leaving the last soldiers on the planet's surface to surrender or suffer annihilation. Cail extricated most of his fleet and what troops on the ground that he could, but never personally recovered from the humiliation of having victory stolen from him.
The fighting at Cerea marked the first time that Federation, Imperial, and Sith forces fought one another simultaneously in a single battle. By total number of ships and soldiers involved, this was also the largest battle in galactic history since the Fall of Coruscant in 9 ABY. The Federation defeat here signaled the end of Federation control of any space west of the Corellian Trade Spine and south of the Great Gran Run (excluding parts of the southerly Javin sector). Cail's defeat here inspired him to launch the famed Campaign of One Thousand Systems, in which he decisively defeated Sith forces for the first time in the Galactic Civil War.