Trevor Sorensen's Star Legions (1992)

Star Legions is the third installment in the Star Fleet gaming universe. Star Legions is much narrower in focus than its predecessors, though; you are charged with managing the planetary invasion forces of the Krellan Empire against the evil (good?) United Galactic Alliance. The result is a bit like playing Empire in a sci-fi environment. Success in the initial invasions means promotions, personal honors, and even greater armies to command in future campaigns.