Established in 1945 in the aftermath of World War II, its founders hoped the UN would lead the nation-states of Earth to communicate more openly with one another, averting war or conflict as best as possible. By 1951, the UN was based in New York City, New York, Earth.
In 1996, after a devastating attack during the Eugenics Wars, leaving thousands dying or dead from a non-curable illness from a biogenic weapon, the UN had the bodies cryogenically frozen and launched into Earth orbit in cryosatellites in the hope one day a cure could be found. (Star Trek: The Cantabrian Expeditions)
- In some continuities, the "old" United Nations was dissolved during the Eugenics Wars, with the New United Nations forming in the wake of the wars. (Star Trek: Avenger: "The Essential Process")
In FASA continuity (all of which was established prior to TNG: "Encounter at Farpoint" and Star Trek: Enterprise), the UN maintained a military/exploration arm called the United Nations Space Force (UNSF). Spacefaring vessels under the auspices of this arm had their names preceded with the designation UNSS, for United Nations Space Ship.