I think the point is: no one any longer knows and written material surviving the incident and made directly after are too filled with propaganda to be reliable.
That is part of the bleak backstory as far as I'm concerned. The world went to hell, no one remembers exactly why or whose fault it was and the same mistakes get repeaten again and again.
FOs 1, 2 and 3 all convey conflict in some scale or another, and a struggle for survival. And the reasons behind those are the same reasons that sparked the devastation in the first place. Desire for power, greed, overwhelming fear or simply a preparedness to do anything necessary to make the tiny corner you live in slightly more bearable and frak everyone else. Despite the devastations and post-apocalyptic horrors, humanity never changed. And as long as humanity never changes... War never changes.
Also keep in mind the FO2 opening: "The details are trivial and pointless and the reasons, as always, purely human ones."