One month after the Battle of Endor in 4 ABY, the New Republic began a campaign to liberate the galaxy from the Galactic Empire. The Fourth Fleet, under the command of Admiral Voon Massa, operated out of the New Republic redoubt of Bothan Space into the Slice, securing the key industrial world of Druckenwell on the Corellian Run in 4 ABY, and in 5 ABY, fighting the grueling three-month Milagro campaign against Imperial forces led by Admiral Uther Kermen.
After securing the Milagro system, the Fourth Fleet advanced and captured the Spirana system from the Galactic Empire, giving the New Republic a foothold in the Inner Rim. There they consolidated in preparation for the resumption of the offensive the next year.
In 6 ABY, the New Republic Fourth Fleet advanced from Spirana into the Denon system, engaging Admiral Kermen's Imperial fleet over the ecumenopolis world. The battle was a savage engagement in which Admiral Massa was killed, but his second-in-command, Admiral Chel Dorat, successfully broke the Imperial lines, driving Admiral Kermen from the system.
The costly New Republic victory advanced its front on the Corellian Run to the edge of the Colonies and secured the crossroads of the Run and the Hydian Way. Together with the First Fleet's defeat of Warlord Prentioch at Bomis Koori IV, and the Third Fleet's victories at Reytha, Uviuy Exen and Palanhi, the capture of Denon advanced Admiral Gial Ackbar's plan to encircle the Core Worlds in preparation for the capture of Coruscant.