Earth in the near future is plagued by a violent war that inevitably ends with the use of nuclear weapons. Nuclear fallout renders the Earth nearly inhospitable. Having the proper technology, humanity leaves earth and begins colonizing other planets or satellites like the moon. Humans begin to survey other systems in space for other habitable planets, leading the search are several organizations, including companies like Helghan.
It doesn't take long to find the two planets in Alpha Centauri. Earth sends a massive fleet to Alpha Centauri, but all vessels and lives are lost durring a violent solar storm. Earth, broken and broke, auctions off the system to the highest bidder in which the Helghan Corp wins.They colonize the two planets, calling the first Vekta (in honor of the company president). Vekta was a planet much like Earth, with vast oceans and flora dominating its surface. It served as a base for all Helghan activities. The second planet was dubbed Helghan (named after the company). Helghan was inhospitable and had little strategic value, but served as an outpost for Vekta. All the other colonies began to recognize the strategic power of Alpha Centauri and exploited its advantage, other companies began passage through the tax system and to profit from their privileged position. Of course, this opportunity eventually triggered a reaction among the various organizations, including the leading military organization ISA. In an impulsive action, ISA threatened Vekta with an embargo that stops allowing them to exercise their right to dominate the territory. Refusing to do so, company Helghan ends up suffering a seige after offering very little resistance to the power of the strategic fleet ISA. Vekta is surrounded and eventually invaded by the ISA. The companies settlers are expelled to the inhospitable planet Helghan. ISA takes care of Vekta enjoying all the strategic value of this planet and made it their property. However, in Helghan stands a charismatic leader who takes advantage of the situation similar to the aftermath of World War I to form the Helghast Empire and prepares a fierce campaign to recover what is rightfully his: Scolar Visari. And here we go into the events of the first game Killzone (PS2). The ISA continues to assert its powerful military wing, even undercover to sabotage their operations to completely annihilate the attempted invasion of the Helghast to their home planet. Vekta is again recovered by the ISA after intense battles on the ground that included some of the Helghast desperate attempts to kidnap key members of the ISA, according to the events of the game Killzone: Liberation (PSP) that culminate in the expulsion of the finalization of Vekta Helghast. Defeated but still resolute the Helghast continue their propaganda campaign as a driving force to break up the military power of the ISA. Eventually, the ISA troops decide to strike a heavy blow by invading Helghan and try to annihilate the rest resistant. But the fact that the Helghast planet has a harsh enviroment it makes the Helghast formidable adversaries. As Visari himself claims, the Helghast have become more than human. (Note: page does not contain the story / events that transpired in KZ 2 and KZ 3)
For the complete history of Killzone, visit http://www.killzone.com/kz/storyline.psml