The Galactic Empire carried out a massacre on Kashyyyk, the home planet of the Wookiee species, at some point before the Battle of Endor. That event almost convinced Mon Mothma, Chancellor of the Alliance to Restore the Republic and enemy of the Empire, that diplomatic action had become completely useless, and that she should start training as a fighter pilot. When the Alliance stood on the threshold of battle, ready to assault the Empire's DS-2 Death Star II Mobile Battle Station battle station, Mothma mentioned the Kashyyyk massacre to Leia Organa, explaining the influence that event had had on her at the time.
The massacre on Kashyyyk was mentioned in Return of the Jedi: Beware the Power of the Dark Side!, Tom Angleberger's retelling of Star Wars: Episode VI Return of the Jedi.
The massacre on Kashyyyk was mentioned in Return of the Jedi: Beware the Power of the Dark Side!, Tom Angleberger's retelling of Star Wars: Episode VI Return of the Jedi.