|Military||United Colonial Army|
In 2055, an oil shortage triggered a global meltdown that resulted in a world war. When the dust cleared, and with Earth depleted of natural resources, it became apparent that if humanity were to survive, new worlds would have to be colonized. A coalition of Earth's wealthiest nations and companies was formed, termed the United Colonial Nations.
Through colonization of the Terran Solar System (including Earth's moon), and star systems beyond such as Alpha Centauri, human life on Earth was able to endure and eventually thrive. The current population of Earth is about 25 billion people. Due to the Earth being majorly overpopulated they have to drain the entire Mediterranean and have entire floating green cities in the Atlantic and the pacific and the government has offered incentives for people to move to other planets such as Mars or Vekta to usually find a low skilled job such as mining or a street sweeper as the slums of earth are rapidly growing in the poorer regions such as South India, Central Africa and Central America. 
As of the Second Extrasolar War, Earth remains the capital world of the UCN. During the conflict it was the target of an intended petrusite bombardment by the Helghast, but ISA forces were able to foil the attack before it could be launched.
- In Killzone 3, Captain Narville describes the crater left by Red Dust as "the size of Kansas", implying that the United States of America, or at least Kansas in some way, still exists by 2360.
- ↑ 2013-02-28, The Killzone Universe: Complete Timeline & Backstory. NeoGaf, accessed on 2013-05-17
- ↑ Killzone 3