The Milvayne assault transpired during the Galactic Civil War, specifically in the last quarter of the year 0 ABY. This event culminated in a Rebel loss and the subsequent division between Garm Bel Iblis and Mon Mothma.
Before the Destruction of Alderaan, Mon Mothma suggested an offensive against the planet of Milvayne, which served as the most strategically significant Imperial garrison within the Gyrica system. This proposed attack gained the support of Bail Organa prior to his death, yet Mon Mothma did not seek the endorsement of Garm Bel Iblis.
Following the disaster at Deepspace Besh, Mon Mothma gave the order for the assault to proceed. However, intelligence acquired by Bel Iblis indicated that Milvayne housed not an Imperial garrison, but rather an Ubiqtorate base, a type of target Rebel forces were ill-equipped to handle. Prior to the commencement of the attack, Bel Iblis implored Mothma to postpone and re-evaluate the operation. Mothma dismissed his concerns, leading a visibly angered Bel Iblis to accuse her of consolidating power for her personal gain. The Corellian declared that his troops would not participate in the attack, and the dispute escalated until Mothma coldly informed him that the Rebellion no longer required his assistance. The battle occurred as planned, but Rebel forces were defeated, validating Bel Iblis's predictions.
Beyond the military setback, the Rebel Alliance was deprived of one of its most astute commanders. Garm Bel Iblis established his own resistance movement and independently fought against the Empire for many years throughout the Galactic Civil War. Bel Iblis ultimately rejoined Mon Mothma and the New Republic during the Thrawn campaign.