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* 2269: Cmdr. Spock assumes Kor's IKS Klothos to possess effective cloaking capability. While primitive cloaking screens had been used by Klingon ships as early as 2256, cloaks effective against Starfleet sensors were thought to be an exclusively Romulan technology up until 2268. (DIS: "The Vulcan Hello"; TAS: "The Time Trap"; TOS: "The Enterprise Incident" )
* 2271: Klingon Empire forces led by Kor achieve a memorable victory over the Romulans at the Battle of Klach D'kel Brakt. (DS9: "Blood Oath")
* 2285: At least one Klingon vessel definitely has cloaking capability. As of 2287, all Klingon Birds-of-Prey were known to have a cloak. (Star Trek III: The Search for Spock, Star Trek V: The Final Frontier)
* 2292: According to Geordi LaForge, Romulans and Klingons regard each other as "blood enemies" by this year. (TNG: "Reunion" )
* 2293: After the Praxis disaster, Klingon Chancellor Gorkon pursues a full peace treaty with the Federation but is assassinated by the Khitomer conspiracy, which Romulan Ambassador to Earth, Nanclus, is a part of. Despite this attempt to prevent a Klingon-Federation alliance, Gorkon's daughter and new Chancellor, Azetbur, later concludes the peace at the Khitomer Conference. (Star Trek VI: The Undiscovered Country)
* 2344: The Romulans attack a Klingon outpost on Narendra III. As the Federation starship USS Enterprise-C responds to the Klingon distress signal and subsequently sacrifices itself, this attack caused the Federation-Klingon alliance to grow even stronger. (TNG: "Yesterday's Enterprise" , "Redemption" )
* 2346: With the help of the Klingon traitor Ja'rod of the House of Duras, the Romulans commit the Khitomer Massacre, killing almost all of the 4,000 Klingon colonists on Khitomer. This happened at a time when, according to Worf, "the Romulans were supposed to be our [the Klingon's] allies". (TNG: "The Neutral Zone" , "Sins of the Father" )
* 2350: Romulan forces fail in an attempt to board Klingon General ShiVang's flagship. That same year, later Romulan Praetor Neral's family are killed in a Klingon attack. (DS9: "Once More Unto the Breach", "Inter Arma Enim Silent Leges")
* 2367: Gowron, who is opposing the House of Duras, becomes new Chancellor. His position is quickly challenged but eventually affirmed in the brief Klingon Civil War against the Romulan-influenced, but ultimately inferior, House of Duras. (TNG: "Reunion" , "Redemption" )
* 2374-2375: The Klingon and Romulan Empires become part of the Federation Alliance, jointly fighting and eventually defeating the Dominion with the Treaty of Bajor. (DS9: "In the Pale Moonlight", "What You Leave Behind")
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