- You may be looking for Xeros-9.
The planet was at some point in time attacked by the Morok Empire. Their home planet of Morok was three light years away from Xeros. The Moroks controlled the planet for many decades, creating a museum for the achievements of their galactic conquests. By the time the First Doctor visited the planet, it rarely had any visitors.
The Moroks enslaved the Xerons, who inhabitated the planet peacefully. For years, the Moroks either killed the Xerons or sent them to work all over the galaxy once they were old enough to go. Xeron children were left by the Moroks, as they posed no threat to their rule.
When the Doctor, Ian Chesterton, Barbara Wright and Vicki Pallister arrived on the planet, Vicki helped the Xerons start a revolution, resulting in them reclaiming their planet from the Moroks. (TV: The Space Museum)