The "Planet of Galactic Peace" was a nickname given to the joint Federation, Klingon, and Romulan colony on the planet Nimbus III, a reference to the world's status as an ambitious collaboration between the three otherwise unfriendly governments. Established in the 2260s decade, the nickname of the "Planet of Galactic Peace" eventually became a misnomer, and was applied rather ironically by the year 2287. (TOS movie, novelization & comic adaptation: The Final Frontier)