destroyed, if not directly by the bombs then in the nuclear winter that followed.
I dont mean to sound cheeky here but...
When will you people absorb that not only is Nuclear Winter a debunked theory it is one that did not develop until AFTER the 50s...
According to 50s theoretical science and thus according to Fallout Science! the world would experience radiation that mutates not kills, and scorching heats from greenhouse gases, and desert like lifeless conditions.
Thus in Fallout THERE WAS NO NUCLEAR WINTER.
So no your theory is wrong.
If you guys read the Fallout Bible the strong implication is that most of the worlds smaller governments collapsed prior to the Great War, during the so called resource wars. These wars werent just fought between the EuroCom and the MidEast but fought between rival nations and groups across the world including the US and China.
Because of the loss of fossil resources the poorer smaller nations of the world collapsed, with no discernable government to protect these peoples their countries fell into anarchy. Tore themselves apart - READ as African countries, South America, Anzac, the stupid little nothing island nations etc.
This followed by the great war where nuclear fire wiped out the stronger surviving nations including the SovUnion, China, USSA, EuroCom, India, and the Mid east.
The radiation and greenhouse gasses kicked up by the nukes according to the rules of Science! in Fallout caused a minor global warming effect which parched the lands killing yet more people. The wind appears to sort of "blow" the radiation around much like dust which would explain the effects reaching even remote areas and countries.
If you play the previous games, if you read the bible, hell its even referenced somewhat in F3. Its easy to figure all this out.
There WERE survivors both inside and outside of the Vaults.
Other major nations DID have their own Vaults. UK, France, Germany, SovUnion, China, Japan are the most likely suspects. Though probably not on the same scale as the US.
Canada being an annexed territory probably didnt have any Vaults. The USSA wouldnt have had any reason to fund the building of any.
In the other countries like South Africa, Australia, NZ, etc. You would probably find that population density is slightly higher than in the remains of the US but is in equal dissarray like the US survivors.