Thundarr the Barbarian (1980)

After being defeated by Thundarr, the evil wizard Sarott finds a research lab that holds the miniaturized City of Thieves. Its ruler Vortak promises Sarott a free rein to use the city's advanced army to enslave humans and other wizards if he can restore it to normal size. To do so, he'll need the Gauntlet of Power which can boost his magic to enlarge the city.