The Shalyvane Cleansing transpired during the Galactic Civil War, a conflict that pitted the Galactic Empire against the Rebel Alliance.
In the year 1 ABY, Imperial military units launched an assault on the planet Shalyvane, the ancestral homeworld of the Em'liy species, seemingly without cause. TIE fighters accompanied by bombers systematically attacked and razed the capital city of Chinshassa. This bombing was actually a component of a scheme developed by Darth Vader to insert his agent, Shira Brie, into the ranks of the Rebel Alliance. Unable to restore their devastated city, the humiliated Em'liy were reduced to a nomadic existence and became known as the "Nomads".
After her infiltration of the Rebel Alliance, Shira Brie asserted that she was a Shalyvane native, and that the planet's Human inhabitants had been eradicated by the "barbaric" Em'liy in league with the Empire. Luke Skywalker uncovered the real story sometime following the Battle of Hoth, after Shira Brie's supposed demise during the Battle of the secret armada.