I'll preface this by saying that all I have as far as concrete evidence is that Vault Tec is a shady company/organization
I've arrived at this hypothesis only because.. and I know this is circumstantial at best, but the Vault Tec rep at your door in the beginning of the game definitely knows something is going down and they 'need' your family.
From the moment you open the door.. there's a tinge of nervousness/lets get this done asap to his voice, it defintely makes me think something is happening and soon. It's something you'd expect from someone who's 'in the know' not sayin this Vault Tec guy is in particular.. be he definitely knows your family's importance to the vault. notice how at the gate they don't check off names rather.. advlt male.. advlt female.. infant.
Vault Tec are bastards.. seriously.. they're the type who come off as trying to help people for the greater good but the more you dig the more your realize it's just a front. I haven't been in to one vault (granted I started playing in FO3 so true vets may call me on this) but not a single vault that I've encountered has had a 'good' objective. By that I mean Vault Tec used all of their vaults for social and psycological experiments.
With this in mind you have to question. They spent all this money building all these vaults..... and the threat of war dwindles.. a resource war is so unliekly it makes the premise unbelievable.
Just so we're clear.. our world and Fallouts timeline diverges after the second world war 1945. They went for nuclear energy.... combustion engine technology still existed and we still svck up fossil fuels with reckless abandon today. The war was never over resources.... power is a non issue in a nuclear fueled society.
These so called 'resource wars' are a farce. Vault Tec was building vaults before this was even a forethought. It's impossible to complete as many vaults as they did unless they had some knowledge prior to when 'stuff' was gonna go to happen.
So what exactly was the war over?
Another thing to consider... ever heard of MAD?
It stands for Mutually Assured Destruction if all countries possess nukes fighting wars is moot. The US used 2 nukes in war time and it's never happened again because we as humans realize that we will destroy ourselves with them. Why would fallout humans think any differently?