United Earth was a planetary state created through the unification of Earth in the 22nd century, following first contact with Vulcans in 2063. United Earth continued to exist as a member world of the United Federation of Planets when Earth helped found that interstellar state in 2161. (Star Trek: First Contact, Star Trek: Enterprise)
By the 2150s, the United Earth government was coterminous with all major settlements made by Humanity. This included all territory on Earth itself, after all previous Human governments united into one organization. United Earth controlled all of the Sol system, but in the 2150s, the organization had begun to spread to other nearby star systems.
Planetary bodies that had major Human settlements or military installations on them in the 2150s included:
In the Sol system:
- Mars – Martian colonies
- Several colonies in the asteroid belt (ENT: "Terra Nova")
- Jupiter Station, a Starfleet support facility in orbit around a gas giant, Jupiter (ENT: "Silent Enemy")
- Titan, used for hazardous environment training by Starfleet (ENT: "Strange New World")
In other solar systems:
- Alpha Centauri – Proxima colony
- Deneva – Deneva colony
- Terra Nova – Terra Nova colony (contact lost in 2083, reestablished in 2151)
- Vega – Vega colony
In the first half of the 22nd century, the most significant Human presence in space beyond the Sol system itself was in the form of "Boomers", independent Human traders that formed a merchant marine using crude, generationally-owned starships that took years to travel between destinations. While nominally under the control of the Earth Cargo Authority, by their very nature, the Boomers were frontiersmen without any real oversight from Earth and generally handled their own affairs. In a sense, these small (with approximately two dozen crewmen on the common Y-class freighter) and mobile ship-borne communities could be seen as "colonies" of a sort. During the second half of the 22nd century, as faster warp drives became more commercially available, travel time between destinations was cut down from years to months or weeks, and response by official United Earth Starfleet ships was, for the first time, made a practical reality; the independent frontier lifestyle of the Boomers gradually came to an end. (ENT: "Fortunate Son")
Even after United Earth was formed, many nation-states and confederations of Earth retained their individual identities. These included the African Confederation, Canada, the European Alliance, Russia, and the United States of America. (TNG: "The Naked Now", "The Price", "Conundrum", "Lower Decks"; VOY: "Imperfection")
United Earth had many agencies. This included an early form of Starfleet (prior to 2161), Military Assault Command Operations (MACO), the United Earth Space Probe Agency, and the United Earth Diplomatic Corps, the latter of which was responsible, among other things, for running the United Earth Embassy on Vulcan during the 22nd century. (ENT: "Broken Bow", "The Expanse", "The Forge"; TOS: "Court Martial")
The term "United Earth" was used in relation to a New United Nations declaration of 2036. (TNG: "Encounter at Farpoint") The phrase was used as a name as early as 2067, for the United Earth Space Probe Agency. (TOS: "Court Martial"; VOY: "Friendship One")
- Minister Nathan Samuels (2155; presided over the talks regarding the Coalition of Planets)
- Councilman Jonathan Archer (2175-2183; represented United Earth to the Federation Council; previously ambassador to the Andorian Empire; later Federation President)
The logo for United Earth was designed by Michael Okuda. "For a long time, I was actually dreading designing the United Earth logo," he admitted, "because it was such an important thing [....] But, when it came time to design, you suddenly realize, 'Well, you want to point toward the Federation [in design lineage] and you want to show Earth,' so it's actually created very quickly." (ENT: "The Forge" audio commentary, ENT Season 4 Blu-ray)
In the novel Articles of the Federation, it is revealed that United Earth came into existence in 2130, with the signing of a document called the Traité d'Unification at the Place de la Concorde in Paris, France; the Place de la Concorde later becomes the site of the Palais de la Concorde, the Federation's capitol building. The novel The Good That Men Do followed the notion that the last nation to become part of United Earth was Australia.
The short story "Eleven Hours Out" in the anthology Tales of the Dominion War indicates that United Earth is a parliamentary system, as an unnamed Prime Minister of United Earth is described as touring the devastated city of San Francisco after the Breen attack of 2375, along with the President of the United States and Federation President (established in a subsequent novel, A Time to Kill, as Min Zife of Bolarus). The novel Starfleet: Year One features a character named Lydia Littlejohn, who served as President of United Earth during the Earth-Romulan War. If the apocryphal stories are accepted as being in continuity with one another, this may be an indication that United Earth utilizes both presidential and prime ministerial offices, akin to the systems of the present-day State of Israel or Italian Republic. (In such systems, the President is usually the head of state, and the Prime Minister is the head of government.)
The Star Trek: Enterprise novel Last Full Measure reveals that United Earth was involved in a number of very low-level conflicts with factions on alien planets (not full governments) and a rebellion on Mars in the years prior to the Xindi attack of 2153; MACO forces played a decisive role in those conflicts. United Earth's military is also revealed to have inherited the martial funeral ceremony of flag folding.
According to an unseen It's Federation Day! article created for the Picard family album in Star Trek Generations, Thomas Vanderbilt was the United Earth ambassador to the Federation Founding Ceremony.