The Kollian Dimension was a parallel dimension home to many inhabited planets with their own native species, such as the Fusians. Their timelines were not aligned with Gallifrey's universe, but travel between them was possible, which led to the Frovian of planet Okul trying to conquer the Kollian Dimension at least once.
Later, under the rule of Prince Luj, the seemingly peaceful Frovians spearheaded an effort to sign a treaty with the inhabitants of the Kollian Dimension, whereby their timelines would become aligned with Gallifrey's, permitting easy travel back and forth. Those in favour of the scheme thought it would promote trade and scientific advancement, but Ux became convinced that Luj was deceitful and only wanted to pillage and conquer the Kollian Dimension once it was easily accessible. He hired the assassin Kasgi to kill him before he added hs seal to the treaty. In the end, Kasgi's plan failed, but the Seventh Doctor, who had discovered that Ux's suspicions about Luj were correct, still managed to stop the treaty from being signed. (COMIC: Who's That Girl!)