The Kohm were one of two ethnic groups on the planet Omega IV who, at least a thousand years prior to 2268, fought a terrible viral war against the Yangs. The name "Kohm" was a corruption of the Earth's 20th century word "communist", an example of Hodgkin's Law of Parallel Planetary Development at work.
Physiology and appearance
Kohms were Asian in appearance, and dressed in a manner similar to Mongol tribesmen of Earth. As a result of the biological warfare waged in their past they had extremely powerful immune systems. A benefit of this is that Kohms had extremely long life spans (the father of a Kohm named Wu was over 1,000 years old and still alive), and suffered from no known form of disease.
The biological warfare waged on Omega IV in the distant past nearly destroyed the Communist civilization, and all but did the same to that of the Yangs. The survivors of the two sides engaged in a millennium-long struggle for dominance on the planet. Over that period, Kohm villages were destroyed by the Yangs, until only one such village remained. The Yangs began to mass for a final attack.
The violation of the Prime Directive by Starfleet Captain Ronald Tracey of the starship USS Exeter, who used his phaser to assist the Kohms in battle, stove off defeat temporarily. However, the intervention of Captain James T. Kirk of the USS Enterprise resulted in the eventual sacking of the last Kohm village.
Yang Chief Cloud William promised Kirk that the words of the Yang "Holy of Holies" (the United States Constitution) would be applied to the Kohms as well as the Yangs. This would seem to indicate that at least some Kohms in fact, survived. (TOS: "The Omega Glory")
In the end credits for the episode, one character is listed as a "KOHN VILLAGER", and the closed captions for the episode transcribe the actors as saying "Kohns" and not "Kohms". Also, it sounds as though the actors are saying "cones".
If one wanted to shorten the word "communist", then it would be pronounced with a short ŏ, like "Khom", and not a long ō like "Kohm". On page 66 of the book, Space and Time: Essays on Visions of History in Science Fiction and Fantasy Television, the Asians are referred to a "Khoms" (author: Allan W. Austin).