Wtf? I LOVE Helghast now...
Looking at the backstory of Killzone, you can also draw the conclusion that the Helghast were justified in their invasion of Vekta as it was their original world to begin with. They demanded a toll for ships passing through their system, and offered excellent service in return, the Earth regime, called the UCN, took offense at them working with the territory they sold to them, and invaded. After the UNC defeated the Helghan government, they exported colonists en masse to Vekta and forced the Helghast to resettle to Helghan. Admittingly, that was after the Helghast carried out a guerilla war, but still, you can see why the Helghast are mad at the Vektans and Earth.
EDIT: I decided to check the timeline of Killzone and see how things went down. To roughly summarize:
- The Helghast Corps secures the rights to colonize Vekta.
- Communications between Earth and Vekta are increasingly diffucult, the UCN is formed and installed as a government system for the colonies in the Alpha Centauri system.
- As agricultural output increases and the colonization of Helghan allows for fuels and energies to be exported at high prices, ships travel through the Vekta system at an increased rate. By supplying, maintaining, and refueling these ships, the Helghast Corps makes quite a lot of money.
- Eventually the Helghast Protectorate is formed as communications between Vekta and Helghant improved to the point where communication was real-time.
I will let the situation of that time speak for itself:
Helghan taxes and energy are now pouring directly into the Vektan market without going through the ISA, whilst Vekta provides Helghan with a wider and healthier variety of foodstuffs and luxuries. Employment is at 95% and morale skyrockets on both worlds. A new emblem is created that is symbolic of the mutually dependent relationship between Helghan and Vekta - three interlinked arms labeled Peace, Justice and Freedom.
- A militia is formed, its officiers provided by the UCN/ISA
- As wealth increases, the Helghan Corps wish to take over as the primary government. An expanded charter is written, but the taxes and regulations placed on the coprs by the ISA is still present.
- Eventually, a surplus of taxes, set aside for emergency situations, is used to buy the Alpha Centauri system and place it under the care of the Helghan Corps. The UCN agrees, due to needing finances to support other less-functioning colonies.
- The Helghan system becomes a hub-system which every ship has to pass through to get anywhere. A tariff is placed on these ships, which local ship-owners are exempt from. This inspires some corps to resettle to the Helghan System.
As some can probably already tell, this is pretty much a rhyme on the American revolution.
- The UCN is alarmed by these developments and decide to start building up their Navy to take the Helghan System back.
- Negotiations for a settlement fail, and the First Extrasolar War begins.
- Long story short, after an initial win for Helghast, the UCN push the Helghast ships back and win the war. The helghan administration is shut down, its executives and senior civil servants arrested. Ultimativly, the UCN and ISA decide that the Helghan are too unruly and put the government back in the hands of the ISA. Colonists from Earth are exported to Vekta.
- In response to a guerilla war/terror campaign carried out by the Helghan loyalist remnants, the appointed ISA governeur curtails more and more rights of the first colonist. As a result, many prominent Helghan families pool their resources and request to be transfered to Helghan. Millions of Helghans are transported to that planet.
- In order to avoid footing the bill of this massive resettlement and having to deliver aid to the Helghast, the UCN/ICA declares the Helghan Administration as a sovereign nation, then places it under a blockade until "diplomatic relations are normalized".
- In spite of the harsh environment and the restrictions placed on the Helghans, they gradually begin to thrive. However, as their standards begin to improve, so does the peoples's anger at the restrictions placed upon them by the UCN/ICA.
- A number of industrial accidents (a rather weak term to describe the events), Helghan suffers a 20 year long economic downturn due to the costs of replacing the machinery that was lost and replaced.
- Visary begins to grow into power, breaking the ISA embargo by encouraging smuggling operations that allow for the Helghan Administration to resume selling their fuel and energy. He also expands the military of Helghan, modernizing and improving on its armament.
- The Second Extrasolar War is declared.
A more detailed description is under this link. The whole timeline reads like a futuristic American Revolution gone wrong.
The Timeline of Killzone