Killzone is interesting in how it has a legit good realpolitik sci fi narrative, that's stapled to the back of a jarhead story.
The helgast colonists got invaded and driven off their home of Vekta
[ by the ISA/earth forces and forced to live on a deathworld filled with lightening storms and giant spiders. This happened because they became a superpower that was eclipsing earth in power, trade and tariffs. The ISA are not the good guys, more like earth's attack dogs. They royally fucked the helgast over and hoped they'd die out and become irrelevant on a backwater mining colony. (Also used forced immigration from other colonys to make conditions so unbearable that the helgast had no choice to but to leave)
All of this is very interesting and the timeline is a very good read
https://killzone.fandom.com/wiki/Timeline , but your following most of these games from the grunt ISA perspective. All of the good lore is background noise to the basic story of fighting gas mask mooks.
Sorry, it has been a while since I played Killzone. How are the ISA that retarded again?
They overpromoted the heros from killzone 1 above their qualifications and thought it was a good idea to half ass an invasion without earth support and allow mass immigration of an enemy population back onto Vekta as part of some kind of liberal hearts and minds bullshit. (aged horrifyingly well ) Thing is, I do respect how the ISA's fuck ups have realistic outcomes. There is a legit war is hell vibe going throughout this series, I just dont think it's conveyed very well through the ISA perspective.
Timeline wise there's no way OG killzone is set in the helldivers universe. You could technically make hell divers 2 a prequel to the OG games, (I like the idea of the helgast forming a Molotov-Ribbentrop Pact with super earth) but the helgan are supposed to be in an age of prosperity by that calendar year. Personally Im just going by the super Robot Wars rule where everything exists together in a separate verse somehow.
Im wondering if they will use the black hole to work in crossover worlds or enemies separate from the main map.