The Kohms were one of two ethnic groups who resided on the planet Omega IV, who, were engaged in a terrible bacteriological war against the Yangs for at least a millennium. In an example of Hodgkin's Law of Parallel Planetary Development, the name "Kohm" was a corruption of Earth's 20th century word, "communist".
Due to the bacteriological warfare that both sides had engaged in the Kohms, like their Yang neighbors, had extremely powerful immune systems, which meant that the Kohms had extremely long life-spans, and suffered from no form of disease.
By the 2260s, the Kohm civilization had been all but destroyed by the Yangs and only one main Kohm village remained, which the Yangs were massing to destroy by 2268. However, Starfleet Captain Ronald Tracey of the USS Exeter, who was visiting the planet, decided to use his phaser to stave off the Yang attack in a clear violation of the Prime Directive. However, the intervention of James T. Kirk and the USS Enterprise resulted in the sacking of this last Kohm village.
Following the Kohm's defeat, the Yangs leader, Cloud William, promised that the Yangs' "Holy of Holies" (the United States Constitution) would apply to all, including the remaining Kohms. (TOS episode & novelization: The Omega Glory)