A neutral zone was a volume of space not claimed by any political power. Often, these volumes were created as buffer zones and borders between spacefaring civilizations. In this sense, a neutral zone was somewhat similar to the Demilitarized Zone that existed between the Cardassian Union and the United Federation of Planets. (TNG: "Journey's End")
Romulan Neutral Zone
- See main article: Romulan Neutral Zone
"Klingon" neutral zone
- See also: Federation-Klingon border
In the alternate 2259, a map of a section of the Neutral Zone in the Alpha Quadrant, from a galactic map, was in a collection of graphics and video media that were seen on a powerwall in the offices of Admirals Christopher Pike and Alexander Marcus at Starfleet Headquarters. According to the map, the United Federation of Planets was scanning activity in Sectors 45 to 89. Along either side of the zone, the location of outposts and movement of blue and red forces was depicted. The outpost of each force was represented by a pentagon labeled T167/550, with each movement depicted by an arrow. There was an active conflict in this region. (Star Trek Into Darkness)
A neutral zone also existed along the Federation-Klingon border by 2285, referred to by the Klingons as the Federation Neutral Zone. In 2267, the development of Nimbus III as a "planet of galactic peace" began in the neutral zone. (Star Trek V: The Final Frontier) This neutral zone was violated by Commander Kruge in 2285. (Star Trek III: The Search for Spock)
When Captain Hikaru Sulu offered assistance to the Klingon High Command following the destruction of Praxis, he was told by Brigadier General Kerla that their assistance was not required and to "obey treaty stipulations and remain outside the neutral zone." The neutral zone was again mentioned during the beginning of negotiations between the Klingon Empire and the Federation which led to the Khitomer Accords. Klingon Chancellor Gorkon proposed a peace treaty that would include dismantling of space stations and star bases along the neutral zone. On Rura Penthe, Kirk confessed that he was terrified of the idea, that there would be no more neutral zone. (Star Trek VI: The Undiscovered Country)
While growing up, Geordi La Forge's family was always on the move, some of the time together, sometimes separately. La Forge recalled that he "never knew if I'd be stationed with my father while he studied in the Modean system, or in the neutral zone with my mom." (TNG: "Imaginary Friend")
In dialogue from the revised final draft script of TOS: "Balance of Terror" (the first episode to use the term), "neutral zone" was used interchangeably with "buffer zone" and "treaty zone". Similarly, a scripted line of dialogue that referenced "cross[ing] treaty line" was evidently changed to instead refer to "enter[ing] the neutral zone." Later in the script, the zone's edge was called "treaty boundary".
The term "Klingon neutral zone" was never mentioned on-screen. The nature of the "neutral zone" mentioned in contexts involving Klingons is unclear. A Klingon neutral zone, separate from the Romulan Neutral Zone, may have been created by the Treaty of Organia, and eliminated by the Khitomer Accords. Kirk's statement would suggest there was in fact a separate zone, as the Romulan Neutral Zone remained effective even after the Accords.
The only "real" neutral zones that have ever existed in the world were Neutral Moresnet, the Saudi-Iraqi neutral zone, and the Saudi-Kuwaiti neutral zone, both established in the 1920s and disbanded by the 1990s. It is unknown if Star Trek writers based the Star Trek neutral zones on these two bodies or came up with the term independently. The Korean Demilitarized Zone is very similar to the Star Trek neutral zone.