United Nations

The United Nations (UN for short) functioned as a coalition of Earth nations, which also created international campaigns and programs. The UN co-ordinated many of these efforts from its office in Geneva, Switzerland, the second-largest UN office outside of its New York City headquarters.

20th century
In the late 20th century, the UN put together the United Nations Intelligence Taskforce (later the Unified Intelligence Taskforce) in order to defend the Earth against threats such as the Great Intelligence; UNIT Central Control was placed in Geneva. (DW: The Invasion et al). This was done due to direct appeal by Alastair Gordon Lethbridge-Stewart. (MA: ''Who Killed Kennedy)

In the 1980s, the UN was overseeing a space agency, International Space Command. (DW: The Tenth Planet)

In 1994, the UN's Security Yard gained its own military branch, UNISYC; it would squabble with other UN factions for alien weaponry in 1996. (EDA: Interference - Book One)

2000s
During the 2000s, due to an unspecified incident, the UN possessed the launch codes for the United Kingdom's nuclear deterrent. (DW: World War Three) Due to a sharp increase in alien incidents, the UN increased funding for UNIT under a policy of "homeworld security". (DW: The Sontaran Strategem) It also went into emergency session when faced with such apocalyptic events like the Moon heading towards Earth. (SJA: The Lost Boy)

In 2009, the United Nations surrendered the Earth in the face of a massed Dalek assault. (DW: The Stolen Earth)

Later history
In later years of the 21st Century, the United Nations possibly replaced UNIT with UNISYC (EDA: Alien Bodies) and/or PRISM (PDA: The Indestructible Man). It possibly transformed into a world government. (DW: The Enemy of the World, PDA: The Indestructible Man)

Behind the Scenes
After the broadcast of Aliens of London, it was announced that the United Nations were no longer happy to be directly associated with UNIT. The term "UN" could, however, be used as long as it wasn't stated what it stood for. Subsequent stories, UNIT's name has not been explained. Later it was shown to stand for United Intelligence Taskforce.