Mind you, the NCR has also been at war with the Brotherhood of Steel while all of this has been going down, years before New Vegas even begins, despite formerly being on such good terms with them that one of the first five states in the NCR was named after BoS's founder Maxson.
Pretty much half the main storyline of New Vegas has you running around trying to woo over half a dozen different factions into fighting for you or for someone else and Yes Man gets super passive-aggressive when you burn bridges or get other groups to align against you.
Honestly, after playing NV, Fallout is way more cynical about human nature than I remember it being, and given the times we are in right now, it's still not nearly cynical enough. If anything, a character like Aaron Kimball is too horrifyingly realistic.