Klingon Civil War

In 2367 Chancellor K'mpec of the Klingon High Council was poisoned, and Captain Picard, acting as Arbiter of Succession, had to choose between two claimants: Gowron and Duras. Duras was killed by Worf in a ritual act of vengeance, but his sisters Lursa and B'Etor later put forward Duras's young illegitimate son, Toral, as a rival to Gowron, who had been installed as chancellor.

When Picard ruled Toral's claim invalid, the Empire split into civil war. Worf resigned his Starfleet commission to fight beside his brother Kurn for Gowron, in return for the restoration of his family's honor. The Duras faction had a hidden ally: the Romulan Star Empire, acting through the commander Sela, who was supplying the rebels in the hope of breaking the Federation-Klingon alliance.

Picard organized a Starfleet blockade along the Romulan border, using a tachyon detection network to reveal cloaked ships. Exposed, the Romulan convoy turned back, and the Duras forces collapsed early in 2368. Gowron secured his position as chancellor, and Worf, spared Toral's life, returned to the Enterprise.