Klingon Civil War
The Klingon Civil War was a conflict fought from late 2367 to early 2368 over the right to choose the next Chancellor of the Klingon High Council and de facto leader of the Klingon Empire. The war was fought between forces loyal to Gowron, the legally appointed candidate, and the supporters of the House of Duras, led by Lursa and B'Etor. The war was a decisive victory for Gowron, but it was achieved only through indirect assistance from the United Federation of Planets in exposing covert Romulan assistance to the forces of the Duras family.

Prelude 

The conflict had its roots in the reign of K'mpec, the longest-lived chancellor of the Empire. Although K'mpec ruled with an iron fist and managed to keep peace within the Empire, his influence began to wane as he grew older, and two opposing factions began to develop. The first faction, led by Gowron, favored the continuing alliance with the Federation, while the second faction, led by Duras, sought to establish a more independent and aggressive policy for the Empire. Duras had support from a large majority of the High Council, while Gowron's support came largely from political outsiders and military personnel.

When evidence surfaced that Ja'rod had betrayed Khitomer to the Romulans, K'mpec conspired with Duras to shift the blame to Mogh in an attempt to prevent a civil war, leading to the discommendation of Worf. This action, however, only postponed the conflict.

Tensions came to a head in early 2367 with the sudden revelation that K'mpec was dying. He had been slowly poisoned by Veridium Six that had been introduced into his bloodwine. Because the killer had not shown his face to his victim, Klingon tradition considered the act to be without honor. Recognizing the corruption that had taken hold in the Empire, K'mpec decided that he could not trust any Klingon with the task of choosing the next leader of the Empire. Therefore, he took the unheard-of action of selecting Jean-Luc Picard, a Human Starfleet officer, as the Arbiter of Succession.

Picard initially refused K'mpec's request, stating that a Starfleet officer had no business choosing the next leader of the Klingon Empire.  K'mpec responded by saying that all he was doing was asking Picard to determine which one of the two challengers killed him, which would eliminate that person from contending for the leadership of the Council. K'mpec further argued that a Klingon civil war would inevitably involve neighboring powers – the Tholian Assembly, the Ferengi Alliance, and ultimately the Romulan Star Empire and the Federation itself. K'mpec pointed out that whoever had so dishonorably killed him – either Gowron or Duras – could not be allowed to rule the Empire. Concerned by the prospect of a massive interstellar war, Picard agreed to arbitrate the dispute.

The process of selecting a new leader for the Empire was almost immediately disrupted when a bomb exploded in the middle of the Sonchi ceremony confirming K'mpec's death. One retainer each from Gowron's and Duras' delegations was killed in the blast.

Picard, wary of K'mpec's warnings concerning the dishonorable actions of either Duras or Gowron, chose to proceed carefully. He revived the ancient ritual of the ja'chuq, in which each contender tried to prove his worthiness to lead the Council, which delayed the final decision long enough to allow the Enterprise crew to investigate the bombing.

What the Enterprise officers found was disturbing: the bomb had used a molecular decay detonator, a type of device used only by the Romulans. Given the past history between the House of Duras and the Romulans – Duras had previously been involved in a cover-up of his father Ja'rod's culpability for the Khitomer Massacre some twenty years before, which was officially blamed on Worf's father Mogh, for which Worf chose to accept dishonor to keep the Empire from splitting up, Duras' house having grown politically powerful – there was now evidence pointing towards one of the contenders. ()

The proceedings were abruptly ended by a fight between Duras and Worf. Duras had killed K'Ehleyr, the Federation ambassador to the Klingon Empire, for investigating into the matter of the Khitomer Massacre and uncovering Duras' father's complicity. Worf, as K'ehleyr's mate, claimed the right of vengeance against Duras, and killed Duras in honorable combat. Although Worf was officially persona non grata within the Empire, the High Council considered the matter closed. With Duras killed and his faction discredited, the way was cleared for Gowron to assume leadership of the Council. ()

Although Duras died in disgrace, his family did not inherit that disgrace. The corruption of Duras had spread to much of the rest of the High Council, who stood ready to support the House of Duras despite the traditional dishonor of its now-dead leader. Lursa and B'Etor, the sisters of Duras, assumed the leadership of the House, and began gathering support to overpower Gowron. They also secured the allegiance of three prominent fleet commanders, swelling their ranks for a possible military challenge to Gowron's leadership.

Gowron requested that Picard, as the Arbiter of Succession, ensure his installation as Chancellor. Picard would not step outside the boundaries of Klingon law, and refused Gowron's request for assistance. He would only assure Gowron that he would respond to any challenges according to Klingon law.

The sisters' power play, when it came, took an unexpected form: they introduced to the Council Toral, a young, previously unknown illegitimate son and heir to Duras. Toral challenged Gowron for the leadership of the Council, and the Council, controlled almost entirely by supporters of the Duras family, backed his challenge.

Picard was thus put in an extremely untenable position – if he accepted Toral's challenge, Gowron would quickly be killed and Toral installed as leader, but if he rejected Toral's challenge, Picard's supposed "Federation meddling" would be used as a rallying cry for the forces of Duras to wrest control from Gowron by force. Ultimately, Picard chose to reject Toral's claim, arguing that Toral had claimed no honor for himself, having fought no battles for the Empire.

Ultimately, however, Picard, as Arbiter, recognized Toral as Duras' son, but concluded that Toral earned no honor or distinctions in his own right and ruled that Duras' claim to leadership had died with him. Toral accused the council of allowing the United Federation of Planets to determine Klingon destiny. He urged them to follow him instead, then left, with most of the council joining him. Gowron was left with few allies and practically no support. ()

Conflict

Soon after, Worf again approached Gowron aboard the , now offering the support of four squadrons loyal to Worf's younger brother Kurn, in exchange for the restoration of his family honor. Gowron was unswayed, as the Duras family controlled most of Klingon Defense Force fleet. Instead, he urged Worf to persuade Picard to convince Starfleet to provide assistance. Worf was unwilling to do this, however the argument was interrupted by a sudden attack.

A Klingon Bird-of-Prey loyal to the Duras had uncloaked and opened fire on the Bortas, and was quickly joined by a second Bird-of-Prey. Although larger and more powerful than a single Bird-of-Prey, the Bortas was now outnumbered two to one and suffered heavy damage, losing disruptor banks and diminished shields in their port quarter. Gowron ordered a distress call to any loyal ships.

The  was orbiting nearby, but Picard instead ordered the Enterprise to move clear of the combat area. Although he had served as Gowron's Arbiter, and Worf was a member of his crew, Picard was unwilling to drag the Federation into a Klingon civil war by going to the aid of the Bortas.

Aboard the Bortas, weapons were quickly restored and Worf assumed the weapons post. Gowron gave the order to return fire, but Worf pointed out that the enemy ships would detect the weapons lock. Instead, he suggested allowing them to believe the Bortas was helpless, luring them in, at which point Worf would aim and fire disruptors manually when they lowered shields to beam over a boarding party.

The Birds-of-Prey moved in, and, as Worf predicted, lowered shields. Worf fired, successfully destroying one ship, but was unable to fire on the other before it raised its shields. The Bird-of-Prey resumed firing, disabling weapons and causing its shields to fail.

Just when the Bortas appeared helpless, a third Bird-of-Prey the  appeared, under the command of Kurn. Pledging loyalty to Gowron, Kurn fired on the first Bird-of-Prey, forcing it to retreat.

Impressed with Worf and Kurn's service during the battle, Gowron, after being installed as chancellor, finally agreed to restore their family honor. There was little time for celebration, however, as the Duras' forces still possessed greater numbers in the bloody civil war that followed. Kurn, an outspoken opponent of both Gowron and Duras, had been persuaded to support Gowron by his elder brother, Worf. Kurn brought the support of three full fleet squadrons with him, which gave Gowron a fighting chance to resist his enemies. Emboldened by this support, Gowron chose to go through with his installation as Chancellor of the Klingon Empire. ()

As his first act as Chancellor, Gowron reversed the discommendation that had been issued against Worf and the House of Mogh, restoring the honor of Worf and Kurn. Faced with a choice to return to duty aboard the Enterprise or fight alongside his brother in support of Gowron, Worf chose to resign his commission to fight under Kurn aboard the Hegh'ta. 

After Picard further refused to involve Starfleet in the conflict, Worf temporarily resigned his commission as a Starfleet, serving as tactical officer aboard the Bortas and later first officer of the Hegh'ta. ()

As the official leader of the Empire, Gowron requested that the Federation send support in fighting the Duras family's forces under the terms of the Treaty of Alliance. Jean-Luc Picard, acting as representative for the Federation, refused to commit Federation resources, fearing that direct intervention would likely to lead to Romulan intervention as well, calling the conflict "by definition an internal Klingon matter."

Although the majority of the Klingon fleet had not yet chosen sides in the conflict, Gowron was seriously outnumbered by the Duras' forces, who controlled at least seven squadrons and had amassed a large fleet near Beta Thoridar. Over the next two weeks, Gowron's forces suffered three major defeats, most notably at the Battle of Mempa.

Although the Battle of Mempa was a major defeat for Gowron, it was also a notable battle because it could have resulted in a complete rout. General Martok first became a revered figure in the Klingon military for his heroic leadership on that day. Additionally, Captain Kurn used a brilliant and unorthodox maneuver of ordering the Hegh'ta to use a solar flare to destroy two pursuing warships. (; )

In the Federation, many eyes were closely watching the reports coming from the battlefields. Although the Prime Directive dictated that the Federation remain neutral in the war, Captain Picard correctly pointed out that if other powers – such as the Romulans – were involved in the conflict, then it would very much be a Federation concern. Picard argued that the unbroken string of Duras victories indicated that they were receiving outside support. Indeed, Picard pointed out that the Romulans had been trying to destabilize the Federation-Klingon alliance for the past twenty years, and it was almost unthinkable that they would remain uninvolved at such a crucial crossroads in the affairs of the Empire.

In a proposal to Fleet Admiral Shanthi, Picard suggested that Starfleet blockade the Klingon-Romulan border and prevent any ships from sending any further, still-hypothetical, support to the Duras family. Using a new technique called a tachyon detection grid, even cloaked ships would be detectable to Starfleet sensors.

Shanthi and the Federation Council authorized Picard's plan, and the  led a 23-ship fleet into Klingon territory to deploy the tachyon net. This action drew immediate protest from the Romulan side of the border, as Commander Sela demanded that the Federation fleet withdraw or be considered hostile and a potential invasion force.

In order to provoke the Romulans into attempting to run the blockade, Picard suggested that Gowron launch a full-scale assault on the Duras' forces in the hopes of forcing the Duras to call for help from their secret allies. The Romulans took the bait, and despite an attempt to evade detection, that was defeated thanks to the initiative of Lt. Commander Data in command of the , the Romulan ships were exposed.

With their connection to the Duras family exposed, Sela ordered her ships to retreat back to Romulan territory rather than risk a fight with both the Klingons and the Federation. Klingon support fell away from the Duras family as knowledge of their collaboration with the Romulans spread, and Gowron's offensive led to a complete victory. In the final days of the war, Lursa and B'Etor fled their base on Qo'noS as it was stormed by Gowron's forces, abandoning Toral to fend for himself. He ended up being convicted of treason by the High Council. In the days following the war Gowron handed the fate of Toral over to Worf.  Worf opted to spare Toral's life, as he'd been little more than a pawn of his aunts, a decision he'd later regret. (; )

Aftermath 
Following his victory, Gowron proceeded to establish strict control over the Empire. He appointed an entirely new High Council membership, including Kurn and several other key allies. Although Gowron's position was threatened by the appearance of a clone of Kahless the Unforgettable in 2369, Gowron was generally treated as the uncontested leader of the Empire until 2375. (; )

Although Lursa and B'Etor fled, their political influence wasn't entirely eliminated. Over the next several years, they attempted to regain their former status by making an effort to raise funds with which to hire mercenary armies, or trying to obtain weapons with which to blackmail the High Council. Commander Benjamin Sisko mentioned the civil war to Odo when Lursa and B'Etor arrived on Deep Space 9 in 2369. Lursa and B'Etor were finally killed in 2371, when their Bird-of-Prey was destroyed by the Enterprise-D in orbit of Veridian III. Toral also made an attempt to regain power in 2372 by seizing the Sword of Kahless, but he was thwarted by Worf, Kor, and Jadzia Dax. (; ; )

For his efforts in ending the war, Captain Jean-Luc Picard received the Rising Phoenix award. ()

de:Klingonischer Bürgerkrieg
Conflicts