In 2266, the Romulans tested Federation resolve by sending a Bird-of-Prey to attack Federation outposts along the Neutral Zone. An ensuing peace treaty established the Romulan Neutral Zone, after which the Romulans had no substantial contact with Humans for a century.

Open war erupted between Earth and the Romulans in 2156, ending four years later with a humiliating Romulan defeat at the Battle of Cheron.

( ENT: ' Babel One', ' United', ' The Aenar') The effort, however, backfired, as their involvement was exposed by Enterprise and spurred the formation of an alliance between the Humans, Vulcans, Andorians, and Tellarites, the nucleus of what would become the United Federation of Planets. ( ENT: ' Kir'Shara') Recognizing the growing threat posed by Earth, the Romulans attempted to incite war in the region by attacking civilian shipping using disguised drones. ( ENT: ' Minefield') Relations between the Empire and United Earth deteriorated as the Enterprise crew thwarted a Romulan plot to subvert the Vulcan High Command. In 2152, the Romulans came into contact with the Human starship Enterprise. ( TNG: ' Gambit, Part I' Star Trek Nemesis) The development of warp drive enabled the Romulans to expand their state into a Star Empire. They settled on the planets Romulus and Remus, subjugating the native Remans in the process. The Romulans originated from dissident Vulcans who rejected Surak's philosophy of peace, during the Time of Awakening and emigrated from their homeworld around the 4th century.

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