For as much as it presents itself as a vision of a utopian, idealistic society, much of Star Trek remains defined by its relation to conflict. There’s the lingering question over Starfleet’s values as a military organization or a scientific exploratory force, or defining conflicts like those against the Klingons, the Borg, and the Dominion that form major pillars of Star Trek lore. But that’s always been the case, and for nearly 60 years, Star Trek‘s early days have been defined by one conflict above all: one that continues to shape and fascinate the series to this day, even though it’s never actually been portrayed on screen.

The Earth-Romulan War has become one of Star Trek‘s most enduring mysteries largely for one reason alone: that its very existence was introduced in what would go on to become one of the most revered episodes of Star Trek ever made, “Balance of Terror.” The 14th episode of original Trek‘s first season, “Balance” introduced both the audience and its heroes alike to the Romulan people, as well as teased the details of the deadly conflict between them and Earth. But it also laid the groundwork for just why the conflict has spent nearly six decades off-screen in Star Trek with the revelation that the Romulans were so secretive, no human ever actually made visual contact with a member of the species until the events of the episode, itself set over a century after the conclusion of the war.

That singular choice has defined the conflict’s place in Star Trek storytelling ever since. The franchise has come close—apocryphal books have filled in their own versions of the war in broad strokes, and both cancelled projects, such as the initial plans for Star Trek: The Beginning or even, as we learned last week, Scott Bakula and Michael Sussman’s plans for a potential post-Enterprise spinoff, Star Trek: United, have wanted to lift the lid on it. But even now, part of what makes it so alluring to fans is that we know so little about it.

That doesn’t mean we know nothing, however.

Prelude to Conflict

Romulan frustration with United Earth began to reach a fever pitch in the early 2150s, as the exploratory and diplomatic mission of the NX-01 Enterprise effectively turned humanity into a diplomatic superpower. By the middle of the decade, a war-torn Alpha Quadrant had largely resolved into a tense but peaceful field of diplomacy between the most prominent species in interstellar society (the Vulcans, the Andorians, and the Tellarites) in large part due to the negotiation efforts of Captain Archer and his crew.

This greatly displeased the Star Empire, which relied on a volatile galaxy to keep its own operations covert. The Romulans increased attempts to reopen wedges between the major powers of the quadrant but also faced an internal reckoning within its own borders: an increasing desire to see the Romulans and Vulcans reunited as a singular society. While we know that the Romulan and Vulcan peoples eventually achieved reunification at some point before the 32nd century, the version being looked to in the 2150s was very different: Romulan agents working with the head of the Vulcan High Command, V’Las, attempted to surreptitiously support the administrator’s plans for a Vulcan invasion of Andoria, which in turn would lead to Vulcan submitting to reunification under the behest of Romulus. But again, V’Las’ attempts to bring Vulcan and Andoria into conflict were exposed by the efforts of Archer and the Enterprise, setting back the Romulans’ influence on their ancestral homeworld.

The Star Empire escalated plans with the Babel Crisis in 2155, launching drone ships piloted remotely by telepaths. Targeting Tellarite and Andorian vessels on the borders of the two powers at the height of trade negotiations between the two worlds on the planet Babel, the Romulan drone ships were capable of using multispectral emitters to visually mask their appearance, allowing Romulan agents to sow discord among the Tellarites and Andorians by posing as each other to attack trade routes.

The Romulans’ plans backfired, however: the Babel Crisis was thwarted by the combined efforts of United Earth, Tellar, Andoria, and Vulcan, who formed a joint operation to combine a fleet of ships from all four species to track and locate the drone warships, ultimately defeating them. Instead of inciting renewed conflict throughout the Alpha and Beta Quadrants, the Romulan effort ultimately stabilized the region altogether. Shortly after the crisis came to an end, representatives from humanity, the Tellarites, the Andorians, and the Vulcans convened a conference that would eventually lay the groundwork for the Coalition of Planets, an unprecedented interstellar alliance, later that same year.

The Four-Year War

The emergence of the Coalition of Planets was what ultimately pushed the Romulan Star Empire into open conflict, with the Earth-Romulan War beginning in earnest in 2156. Little remains known about the exact nature of the war, other than that it was seemingly largely waged between the Romulans and United Earth forces. Just over a century after its conclusion, when tensions between Starfleet and Romulus arose, Spock described the conflict as primitive by contemporary standards: ships on both sides of the war were vastly inferior to the standards and size of those used by galactic powers in the 22nd century and incapable of holding prisoners of war, and the majority of the weaponry used was still atomic in nature.

This totality of destruction also meant that both the Romulans and the Coalition powers never actually made visual communication with either side over the four years the conflict dragged on, keeping the Romulans’ general identity—and their ancestral connections to the Vulcans—a secret throughout the war.

What is known about the Earth-Romulan War is that it concludes four years later in 2160 after the Battle of Cheron. Again, the circumstances of that battle are largely unknown outside of two factors: that it was fought between the Romulans and a Human/Vulcan/Andorian/Tellarite alliance (presumably under the banner of the Coalition of Planets), and that the battle was an absolute disaster for Romulan forces. Defeat was near total, and memory of how poorly the battle for the Star Empire went would continue to have military and political ramifications for centuries.

Centuries of Aftermath

The end of the war would have huge ramifications for the Alpha and Beta Quadrants for generations to come. A peace treaty, agreed to over subspace radio between Starfleet and the Romulans, led to the establishment of a Neutral Zone between the borders of allied space and the Star Empire, an area of space neither side could move ships into or through without it being seen as an act of war. Little is known as to how the Romulans monitored their side of the Zone, as the Star Empire retreated from astropolitics for the best part of a century in the wake of the war’s conclusion. However, Starfleet monitored its side of the zone with the establishment of outpost monitoring stations housed on asteroids.

A year after the conflict concluded, the Coalition of Planets was dissolved to make way for the formal founding of the United Federation of Planets in 2161. Now led by President Jonathan Archer, the Federation ushered in a new age of galactic politics, as more and more member worlds joined the four founding planets of Earth, Tellar, Andoria, and Vulcan, and Starfleet became its primary interstellar task force.

It wouldn’t be for another 100 years that the Romulans would test the constraints of their peace treaty with the now-Federation, when an unnamed Romulan commander attacked and destroyed four of Starfleet’s monitoring stations along the edge of the neutral zone. Ultimately destroyed in turn by the U.S.S. Enterprise, the Federation’s flagship, the incident marked the first known visual communication between humanity and the Star Empire, exposing the Romulans’ visual similarity to the Vulcans.

This waxing and waning of Romulan involvement beyond the borders of the Star Empire would persist until the Empire’s collapse in 2387 after the star of the Romulus system went supernova, destroying both Romulus and its sister world, Remus. For a brief time in the 22nd century, the Romulans formed diplomatic relations and trade deals with their Beta Quadrant counterparts in the Klingon Empire, and in 2311, conflict between the Federation and the Star Empire briefly erupted in the Tomed Incident, which concluded with a new treaty that reinforced the Neutral Zone’s borders and prohibited the Federation from researching ship-based cloaking technology, a key technological advantage long held by the Romulans, as well as the Star Empire’s return to isolation.

Only one major incident reflected an act of diplomatic alliance between the Federation and the Romulans across those centuries of general distrust: in 2374, at the height of the Federation’s war against the Gamma-Quadrant-based Dominion, the Romulans were pushed to enter the conflict alongside the Federation after years of neutrality when a high-ranking member of the Romulan Senate, Vreenak, was seemingly assassinated by Dominion forces in an attempt to cover up evidence of Dominion and Cardassian plans to invade the Star Empire. The Romulans would go on to play a pivotal role in alliance with the Federation and Klingon Empire for the remainder of the war, even providing cloaking devices to Starfleet vessels like the U.S.S. Defiant in a limited capacity.

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