Romulan Star Empire

The Romulan Star Empire was the primary state of the Romulan people. Its capital was the planet Romulus in the Beta Quadrant and it was governed by the Romulan Senate. A highly secretive state the Romulan Empire was known for its xenophobic and hostile attitude towards other species.

History
During the 2150s the Romulan Star Empire went to war with United Earth. With its defeat a neutral zone was established between the empire and Earth. The empire then entered a prolonged period of isolation. 

During the mid-23rd century, the Romulan Star Empire left its isolation, returning to the galactic scene. During this period it joined in an alliance with the Klingon Empire trading its cloaking technology for powerful Klingon D7 class cruisers. 

The Romulan-Klingon Alliance would eventually come to an end in 2292. 

In 2311, the Tomed Incident between the and the Romulan Empire led to the Treaty of Algeron between the two powers. One of the components of the treaty was a ban on the Federation developing and using cloaking technology. Following this the Romulans again entered a extended period of self imposed isolation. 

While the Romulans had mostly left the galactic scene they periodically clashed with their neighbors. Following a series of attacks by an unknown force, later believed to be the Borg, along the Neutral Zone led to the Romulan Empires re-engagement with the Federation. 

Initially after the Dominion entered the Alpha Quadrant the Romulan Empire stood against them, deploying starships to Deep Space 9 to join the Klingon and Starfleet forces to defend against what they believed to be a Dominion attack against the space station. Several month later the empire signed a nonaggression pact with the Dominion and when the Dominion War began in earnest in late-2373, the Romulan Empire was not involved. 

In mid-2374, the Romulan Star Empire entered the Dominion War joining the Federation Alliance. The Romulans' entry into the war was sparked by the assassination of Senator Vreenak and the discovery of a Cardassian isolinear rod that seemed to show a Dominion plan for a surprise invasion of the empire. The Romulans assumed that Vreenak had come across the information during a visit to Cardassian space and had been killed by the Dominion to prevent the information from returning to Romulus. In reality, the information on the rod was a forgery as part of a plan by Starfleet Captain Benjamin Sisko to bring the Romulans into the war on the Federation's side. 

In 2375, the Federation Alliance won the Dominion War forcing the Female Changeling into surrendering her forces. In the aftermath the Cardassian Union was divided into protectorates between the major allies including the Romulan Star Empire. (' novel: ')

In 2379, the Romulan Senate was assassinated and Shinzon backed by part of the Romulan military and the long subjugated Remans took power. Shinzon almost took the empire to war with the Federation with his plan to attack Earth and devastate it with a thalaron radiation weapon. Shinzon's plans were thwarted and he was killed during the Battle of the Bassen Rift. 

Territory

 * Romulus and Remus
 * Achernar Prime
 * Algeron system
 * Artaleirh
 * Constanthus
 * Derassa IV
 * Devoras system
 * Diodor sector
 * Eloh
 * Gevallos III
 * Kevratas
 * Onias sector
 * Rator III
 * Serus III
 * Tareus IV
 * Unroth system
 * Unroth III
 * Vela Expanse
 * Tharcel Prime

Agencies

 * Romulan Guard
 * Romulan Star Navy
 * Tal Shiar
 * Tal Prai'ex
 * Tal Diann

After Shinzon's death, the Empire was briefly fractured in two. In 2384, the Romulan Star Empire was led by Tal'aura while Donatra ruled over the Imperial Romulan State until Tal'aura's death. In 2385, both fragments were reunited, with Chulan as Praetor. 

A major blow was dealt to the Empire in 2387, when Romulus was destroyed. The Federation offered to supply relief to the Empire after the destruction of the planet. (: "Gogmagog", "Relief and Refuge")

Star Trek: 001
During the 28th century, the Romulan Star Empire entered an alliance with several other regional powers to stand against the Federation, which they saw as corrupted by the long term influence of Section 31. The Alliance and the Federation eventually went to war. (Star Trek: 001: "Red Sand, Dark Tide")

Star Trek: Arcadia
In 2382, the Romulan Star Empire was succeeded by the Romulan Republic.

🇸🇹
In 2379, the Romulan Commander L'mar, attempted to continue his cloning research using skin samples he collected from Captain Benjamin Kelsoe. His experiments failed and he eventually abandoned his ship, becoming an outlaw and seeking work with Tyson Calok. ("Beware Romulans Bearing Gifts", "The Crossing", "Prime Target")

In early 2381, the Romulans expressed interest in the energy particles located in the Venka Nebula located in the Oralian sector. ("Unresolved Matter")

In late 2382, the Romulan Star Empire entered into the Coalition War on the side of the after the Federation sent Ambassador Spock to negotiate the treaty with them. ("Dawn")

The Romulan Star Empire was replaced by the Romulan Star Republic. 

After the Battle of the Bassen Rift, the Star Empire chose to approach the Federation more peacefully. The Romulan Star Navy and Starfleet established an officer exchange program which led to the USS Gustav P. Remington (NX-86753) taking on Trevak as her first officer. However, many hard-liners within the Romulan government were opposed to the peace and chose to break away, forming the Romulan Confederacy and taking significant parts of both the Star Navy and the Tal Shiar with them.