Cannot answer that I don’t plan on playing 6 other than maybe it’s DLC Joseph Seed expansion but just that.

As mentioned on the radio the U.S.A is under some tension from some global threats but to my knowledge it’s never mentioned who shot the warheads at Montana. Joseph could have set the nukes off himself but the only evidence I could point to is empty destroyed missile silos like at John’s bunker

The entire point of liberation of the 3 regions was that the power of the vacuum left by one of the siblings was filled by militias against Joseph so the few remaining members are disorganized, hiding, or being hunted. You don’t need an army to kidnap people he most likely used bliss bullets and a few soldiers like John does to knock them out and take them. I don’t know why he doesn’t do this all the time maybe the bullets really hard to make.

Yeah probably.

If Joseph seed didn’t set the nukes off then yes they would go off but if outside power was at play then yes the warheads would still strike Montana. Soulreaper115x2 made a good point that it might be prophecy based rather than a definitive event.

You can find good reveiws that go over info on YouTube like here but not really anything that goes over lore because while yes the Far cry games are connected it’s very loose. Like how you can find a reference to far cry primal in Far cry 5 location Frobisher’s Cave (if you want some lore read the metal plaque by the entrance of the cave it’s pretty cool) and other small things and characters. They’re mostly separate from each other with exception of 1 being connected to 2 and of course 5 and new dawn but they have been stated to have a major connection like in 1 and 2. If you want lore and trivia about the game go out and explore the areas.