In 3640 BBY, during the Galactic War between the Galactic Republic and the Sith Empire, Imperial forces attacked the Republic agriworld of Ruan and conducted an orbital bombardment. Under the command of Moff Nezzor, the Imperial Navy devastated Ruan's agricultural production facilities and killed thousands of Republic civilians and personnel.
After a bombing attack on the Orbital Defense Command Center on the planet Ziost nearly killed the Minister of Logistics Davidge, the Minister was ordered by the Dark Councilor Darth Marr to launch additional attacks to put the Sith Empire back on the offensive in the Galactic War with the Galactic Republic. Davidge was also ordered to make use of Moff Nezzor, whom Davidge believed was an unprofessional sociopath, and the Minister was forced to divert resources to Nezzor. The Republic Strategic Information Service learned of the upcoming attack on Ruan through a black cipher, one of the Empire's secure encryption devices that they had recovered during the attack on Ziost, though Supreme Commander Jace Malcom refused to send any aid to the agriworld in order to conceal the Republic's possession of the cipher.
Penetrating deep into Republic space, a fleet under Nezzor's command attacked Ruan—one of the agriworlds that supplied the Republic's capital of Coruscant with foodstuffs and a planet located in the same sector as Coruscant—and wiped out the Republic fleet in the area before conducting a brutal orbital bombardment by capital ships. The attack wiped out most of the production facilities on the surface and killed thousands of civilians in the process, scoring a major victory for the Empire.
Emboldened by his success, Nezzor would attempt to strike at the ship-producing world of Duro not long afterwards, and the Imperial Ministry of War used the battle in its propaganda campaigns in order to reassure the people of the Empire that they were not losing the war.
The battle at Ruan was first mentioned in Chapter 11 of the 2012 novel The Old Republic: Annihilation when Darth Marr orders Minister Davidge to make use of Moff Nezzor, and Theron Shan watches news reports of the battle over a week later while infiltrating the Imperial outpost Reaver Station.