Author's disclaimer: The characters used here are either the creations of those involved in the production of Star Trek in its various incarnations over the years or the author's interpretation of what characters created by those involved in the production of Star Trek would be like in a mirror universe. Their Federation counterparts are seen in Star Trek episodes and/or movies and are the property of Paramount Pictures. I do not own those characters; I am merely borrowing them for a while. No copyright infringement is intended.

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They'd built an Empire together and ruled it by brute force, but Vulcans and humans had fallen out long ago over Spock's efforts to reform the Empire. Many Vulcans had supported those efforts, and because of this most humans blamed Vulcans for their Empire's misfortunes. The latest war had broken out after the Narendra III incident almost twenty years earlier, and it wasn't going well for the Empire. It was rare these days to see a Vulcan on a battleship as anything more than a slave, let alone as Chief Medical Officer. Selar was in fact a slave, but was reluctantly appointed CMO because she was the only one aboard with the medical knowledge who was still alive, and the war made for a shortage of all officers.

That same shortage was one reason her latest patient was still on board. Wesley Crusher hated Captain Picard and Commander Troi because of what they did to his mother. They would rather have disposed of him as well, but the war made someone with his talents indispensable. He also had a curiosity about Vulcans, even though an ancestor had died by a Vulcan's hand.

That ancestor was Robert Wesley, whom Spock had overthrown as emperor almost a century earlier. Right now Selar was treating his great-great-great-grandson for injuries suffered in the latest battle with Alliance ships.

"Why did Spock do what he did?" Ensign Crusher asked as Selar was treating him.

"It's because of what happened with the Halkans," Selar said. "The Empire wanted to use their dilithium in its frequent conflicts with the Klingons, but the Halkans refused to allow this despite the threat of a phaser barrage against their cities. They were prepared to die as a race, rather than be willing participants in the Empire's wars. They also warned that by the time the entire galaxy was conquered, the Empire would no longer be able to endure the collective rage of all its slave planets, and would collapse in a civil war that could destroy the galaxy."

Wesley remembered what he'd been taught about the Halkans in school, how they were secretly allied with the Klingons, that their calls for disarmament and peace were really attempts to leave Earth vulnerable.

An hour earlier the I.S.S. Enterprise's first officer would never have questioned the Empire's orders to annihilate the Halkans. But while his captain and the rest of the away team were returning from the planet's surface, a transporter malfunction had caused them to change places with their counterparts from an alternate universe where Vulcans no longer ruled an empire built by conquest and expansion. They were now members of a united federation with Earth and other planets that Spock had learned about from a mind-meld with one of its officers. Before returning to his own universe, Captain Kirk's Federation counterpart urged Spock to consider the Halkan prediction of civil war, and to try to forestall this by leading a movement to reform the Empire.

Kirk's own landing party materialized inside the transporter chamber just as the counterparts beamed out, and Kirk could tell at once his counterpart had caused Spock to question his loyalty to him. But it was already too late. Realizing Kirk intended to have him killed, Spock was forced to get rid of his captain in self-defense and take command of the Enterprise.

Spock still had two hours to act against the Halkans per a private communication from Starfleet. He decided to make use of this time by beaming down to the planet's surface and sharing his recent experience with them, and learned the Federation and Halkan governments were very similar; the primary difference was size. He sought to have a mining team from the Enterprise allowed to begin operations on the planet's surface in exchange for a promise on his part to work to reform the Empire so that every planet would have a voice in its policies, and by convincing the Halkans they were of more value as a living model to pattern reforms after than as an extinct race, Spock obtained the concessions he had asked for. With a fresh supply of dilithium, he took the Enterprise to Vulcan.

Spock was successful in convincing Vulcan's ruler T'Pau of the need to reform Vulcan's government, and to allow a measure of dissent on Vulcan and its colonized worlds. Despite considerable opposition in the senate, whose members were appointed for life from Vulcan's most powerful business leaders, they were able to organize the first popular elections to this body as vacancies occurred over the next few years. They then set out to create a governing council patterned after Halka's and consisting of Vulcan's praetor, proconsul, vice-proconsul, and representatives elected from each of the Vulcan-colonized worlds. The Halkans elected Tharn, their own council leader, as their representative on Vulcan's council, where their pacifist views found a widespread following. By now Spock was an admiral at Starfleet Command, and had begun to openly advocate extending the reforms begun on Vulcan throughout the Empire. When Wesley became caesar almost a decade after the transporter accident he sought to have Spock arrested on treason charges and executed, but Spock had learned of this, and had engineered a coup to overthrow Wesley before he had a chance to consolidate his power.

Having seized control of the Empire, Spock began to carry out the reforms he had been advocating. He abolished the title of emperor, as well as the Empire's Earth-and-dagger emblem, and ordered that elections be held to expand the council created by the Vulcans to include delegates from each of the occupied worlds throughout the Empire, and Earth was allowed to elect representatives as well. This effectively moved the Empire's center of government to Vulcan, but then everything collapsed.

The basis for the treason charges Wesley had tried to level against Spock had been the influence Spock and other Vulcans had allowed the Halkans to acquire in Vulcan's government. Their calls for disarmament were well intentioned, but this was not a practical approach, and not only because of the Klingons. A large faction in Vulcan's senate that had support from Earth still opposed their planet's reform efforts, and it was to win over this faction that Spock had made Vulcan the Empire's capital. But expanding the council served to expand Halkan influence throughout the Empire as well. Under pressure from the Halkans Spock even agreed to cancel production of the new Excelsior-class battleships, and this alienated Vulcan's senate even further. Spock also miscalculated Earth's reaction to his reforms. Those of Wesley's supporters who had escaped held secret meetings with a number of starship captains to discuss retaking the Empire by force. It was revealed that the Empire's scientists were working on an experimental transwarp engine, which, by enabling starships to travel many times faster, was expected to finally give Starfleet the edge needed to conquer the Klingons. The captains, who included the Enterprise's current commander, Hikaru "Scarface" Sulu, realized the Halkans would lobby to have the transwarp project canceled, and Spock would most likely agree to this. A fleet of starships was soon converging on Vulcan.

Vulcan's defenses were overwhelmed. The Council Building was stormed, killing the council members and Vulcan's own leaders, including Earth's representative who had taken part in the coup. A ruling committee under Admiral Cartwright was formed, with a puppet government installed on Vulcan, composed of senators who took part in the coup, and the Empire's Earth-and-dagger emblem was restored. Spock was sentenced to death, but was able to place his katra into a follower who escaped, and in this state, witnessed the formation of an underground resistance.

"Do you know if they can duplicate what happened with the transporter?" Wesley asked.

"It's been done," Selar answered. "Spock's security team located the device the first crossovers used to return. He used it to send one of his crewmembers to the other side without bringing her counterpart here, once she showed him how Kirk made his enemies 'disappear.' Years later, one of the rebels used it to take his katra to the other side, because Mt. Seleya was under Earth control."

For their perceived efforts to subvert the Empire the Halkans felt the new government's full wrath and were annihilated. Those who perished did not include Tharn, who had died from natural causes shortly after the elections Spock ordered were held.

War broke out with the Klingons almost immediately after Spock was overthrown. The Excelsior project was re-instated, but efforts to utilize transwarp were futile and early Klingon victories were made possible by the Empire's recent upheavals. Klingon forces even captured the Excelsior prototype, but then the explosion of Praxis crippled their own industries and would have led to their being conquered if the Empire's occupation of Bajor hadn't unexpectedly brought it into conflict with the neighboring Cardassian Union.

Like many people who had suffered under Terran rule, the Bajorans had seen their hopes for better living conditions dashed when Spock was overthrown and his reforms scuttled, and formed a resistance group similar to Vulcan's. The Vulcans shared tactics with them, but the amount of Earth-controlled space separating the two worlds made close coordination between the two groups impractical, and the Vulcan resistance largely collapsed as the war led many Vulcans to put aside their differences with Earth. The Bajorans also distanced themselves from their Vulcan allies as they began receiving arms shipments from Cardassia. Encouraged by the Klingon victories and with these weapons, their activities threatened to stir an uprising by the time Praxis exploded, and when Earth sent ships to crush the rebellion, Cardassia intervened. Instead of a technological breakthrough promising a quick victory the Empire was fighting a two-front war, which led to a stalemate. By now many in Vulcan's government were taking a second look at what Spock and others tried to tell them, and they were able to convince both Earth and the Alliance to agree to a cease-fire.

The cease-fire largely held over the next decade. Cardassia and Bajor formed a political union while the Klingons recovered from Praxis, and the Terran Empire developed the Excelsior's Enterprise-B variant. No prisoner exchange took place after the war, and prisoners on both sides performed slave labor.

Most Bajorans had welcomed the chance to join the Alliance and turn the tables on their conquerors. However a number of vedeks and other Bajorans realized that by joining the Alliance their people had become no better than the Terrans had been, and gave shelter to human and Vulcan slaves who had escaped their overseers. Those given refuge included Tuvok, a security crewman on the Excelsior at the time of its capture. The vedeks also made sure slaves who were too young to remember knew about the different way of life that Spock and other Vulcans had tried to offer them.

Both Empire and Alliance knew whose visit had such a profound influence on Spock, and through Spock the Vulcan people as a whole. After overthrowing Spock, Admiral Cartwright ordered that anyone found to have crossed over from the other universe be executed at once to avoid any further "profound effects," and the Alliance agreed this was a sound policy.

Renewed fighting broke out less than two decades later. The Klingons developed their B'rel and K'Vort classes ship at this time, and were able to make enough gains to form a political union with Cardassia and Bajor. Earth forces fell back from Vulcan to defend the shipping lanes between the Alpha Centauri and Terra Nova colonies, and the Excalibur-class ships formed part of this defense perimeter when they entered service. The Vulcans revived their resistance movement as their world was being overrun, and with the help of sympathetic Bajorans located sites in the Badlands where they were able to construct bases undetectable to the Alliance. They were also hidden from the Empire, and this was just as well. By now Earth decided the Vulcans were more of a liability than an asset, and offered a cease-fire that ceded Vulcan. Earth agreed not to give any aid to the rebels, and to turn over to the Alliance any rebels apprehended. The Alliance accepted. The latter clause was not always adhered to, and Vulcans became slaves to both powers.

"Your parents were rebels, weren't they?"

Selar nodded. They had worked with Tuvok's resistance cell, and were apprehended three years after Vulcan was ceded.

The possibility of deliberately crossing to the other universe had not been lost on scientists from the Empire or the Alliance either. Chief Engineer Montgomery Scott raised that possibility with Captain Sulu after Spock left the Enterprise, and they were able to conduct their own experiments on the transporter. It was realized early on that even if the transporter could be rigged as a crossover device there was no way to detect with sensors beforehand where in another universe an object was being transported. They did, nevertheless, figure that they could scan objects in another universe at the moment the transporter was activated and interdimensional contact established. In this way they were able to calibrate the transporter so that if a planet was below the same planet was in the universe being targeted. It was even found possible to send clipped subspace messages to the landing parties, and with Uhura's help they were able to monitor subspace communications in other dimensions for short periods of time. Sulu and Uhura continued these experiments on the Excelsior with help from Tuvok after Sulu was given command of that ship, and earned theta designations following the Excelsior's loss by helping the Alliance conduct its own research. The Empire ordered a number of starship crews to duplicate their work, among them the Enterprise-B crew under Captain John Harrimann. The Enterprise-B crew had a jumpstart over others involved in the project, as Demora Sulu, Hikaru's daughter, was its helm officer. By comparing intercepted communications with the observations of the original landing party, both sides were able to identify the universe the "visitors" had most likely come from. Harrimann was then placed in charge of developing the Excalibur-class ships, which even had a cargo transporter in their shuttle bays capable of transporting a shuttle into the other universe. Shuttle crews would patrol a given area of Federation space, then park at a given time and place, and be transported back. Both sides felt threatened by the prospect of crossovers from the other universe, and might have eventually conducted joint research if another war hadn't broken out.

"The war isn't going well this time, ensign. I've overheard the captain's discussions with both his officers and his superiors, " Selar said. "He may not think I hear those things, but I do.

"After Spock was overthrown the Empire survived because of Praxis. In the war that followed it bought time by offering Vulcan to the Alliance. This time there's nothing left to offer. Or as your people are fond of saying, 'no more cards to play'. They estimate the Empire will fall in about six months, a year at the latest."

"I've been wondering about that myself," Wesley admitted nervously. "I guess you won't be sorry to see us humans become slaves just as your people are."

"I'll be sorry to see you become one of them."