- 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. The Moroks controlled the planet for many decades, creating a museum for the achievements of their galactic conquests. It was noted as the best museum in the galaxy at the time, with many visitors from all over the Morok Empire.
The Moroks enslaved the Xerons, who inhabitated the planet peacefully, focusing on knowledge and science. 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 First Doctor and his companions arrived on the planet, the Xerons were preparing to revolt. The Doctor and his companions helped the Xerons reclaim their planet from the Morok rule. (TV: The Space Museum)