For this operation, the Grand Army of the Republic combined divisions from the Core Worlds to form two new formations—the First and Second Armies. They were collectively known as the Army Group Mortex, under overall command of Jedi Master Ugan Nemix. The CIS' northern front was commanded by Nyranos lij Xikharalik, a Kaleesh warlord, who had command over the defense of the sector—which was defended by the Sixth Army Corps and the Mortex Defense Fleet. On the planet of Nyranos' staff headquarters, Ranroon, his troops were aided by the Ranroon Royal Army.
The campaign lasted for about two months, and resulted in heavy casualties for both sides, though with a Republic victory in the sector. The Republic gained control of the sector but at a cost of around 420,000 casualties (out of it's force of 960,000). The CIS forces had a strength of around one million droids and 200,000 organic fighters. Out of those, around 570,000 droids were destroyed, and 97,000 organic soldiers became casualties.
As the tide of the conflict slowly began to turn in the tide of the Republic, the high command of the Grand Army decided it was time for an offensive into the CIS holdings of the Outer Rim. Plans were drafted, but as more demand were made by the forces on the various fronts, it became apparent they did not have the strength for a full offensive, but only a few operations. As the northern sectors of the galaxy were largely dominated by the CIS, that region became one of the locations considered as a place for an offensive by the Republic army staff. Finally, after much thinking and negotiating with the navy staff, they decided on the Mortex sector as the prime target, as it was the location of the headquarters of the CIS' northern forces. The plan was approved by Supreme Chancellor Palpatine, and a date was set. However, it was set back as many of the needed units were not available at the moment.
With the Chancellor's approval, preparations began. It was decided by the Republic Navy would deploy it's Fourteenth Fleet for this offensive, against the CIS' Mortex Defense Fleet. The Grand Army, meanwhile, created a new command—Army Group Mortex, under overall command of Jedi General Ugan Nemix. It was composed of two new formations: the First and Second Armies. The First had a strength of seventeen divisions, while the Second had a strength of fifteen. The staff thought of deploying the 501st Legion, but they were already demanded by several other commanders, so this idea was quickly thrown out. Two experienced generals, Xaron Majid and Verax Zargon, were selected to command the two individual armies. As it was (falsely) assumed that Nyranos would spread his forces to cover every entrance into the sector, it was planned to have an all out strike through one hyper route, which would be the shortest path to Ranroon.
The Separatist military intelligence got word of the plans, though not the specifics. Nonetheless, Warlord Nyranos lij Xikharalik, a Kaleesh commander that led the CIS northern command, was informed, and had begun preparations. The warlord arranged for the best unit in the north under his command, the 6th Army Corps, to be reassigned to the Mortex sector. The Confederate Navy assigned a well sized fleet, the Mortex Defense Fleet, to oversee the orbital defense of various key worlds in the sector. Nyranos' defense plan revolved around heavily defending several key worlds in the sector as heavily-defended fortress worlds, and keeping the Republic at bay as long as possible—to wear out their forces and make them retreat. In addition to the 6th Army Corps, an local force, from his headquarters on Ranroon, would take part in the defense—the Ranroon Royal Army. The 6th Army Corps commander was General Kummar Ronderu, while the fleet commander was Admiral Cydon Versavis. The commander of the Royal Army was Malik Kardexu.