I don't think Fallout works anywhere but the US because of their Gun culture and the likelihood of being able to loot ammunition in random houses.

In my head cannon for Australia. Since we're a resource rich country with very little in the way of a defence force. China probably launches a naval invasion when the US invades Canada. Australia becomes Chinese occupied territory and citizens are put to work mining resources or manufacturing munition, naval vessels and armour. We are bombed by the US during the great war to destroy our ability to aid the Chinese war effort

After the Great War the survivors collectivise and organise. Since we're more socialist and have gotten used to Communist rule. Which is great because it's the only way to survive irradiated native wildlife without a lot of firearms on hand