Although it's a fascinating bit of early Star Trek continuity, the war between the Romulan Empire and United Earth has never been realized on-screen, representing a huge missed opportunity for the franchise. In Star Trek: The Original Series season 1, episode 8, "Balance of Terror", Captain James T. Kirk (William Shatner) encounters the Romulans for the first time since the end of the Earth-Romulan War, a century earlier. The episode explores prejudice as despite a century having passed, certain Enterprise crew members are suspicious of Spock (Leonard Nimoy) due to his genetic similarities to the Romulans.
Star Trek: Strange New Worlds revisited this when Captain Christopher Pike (Anson Mount) attempted to outrun his tragic fate, and inadvertently changed TOS' "Balance of Terror". However, the Star Trek franchise itself has never properly explored this conflict from the Federation's history. Executive Producers Manny Coto and Brannon Braga told attendees of the annual Star Trek convention in Las Vegas in 2009 that, had it not been canceled, Star Trek: Enterprise season 5 would begin "whispers of the Romulan War" but this sadly never came to pass. While other attempts have been made to explore the war, it remains one of Star Trek's biggest missed opportunities.
