Your US/WWII premise is flawed because you are specifically cherry-picking an event that we know happened and using it as a basis for a hypothetical question. This is not a valid comparison because we do not know for historical fact Australia held out of joining the world government until 2150.
False. There is no significance to whether the events are fictional or factual. The question itself always establishes which parts are to be taken as fact and which are to be speculated upon.
You're ignoring the definition of the word "say" in Crusher's comment.
False. Its only "definition" there is to establish that Australia was but one out of
multiple possible old nation states that could have refused to join. Australia and those other nations all would by the wording of the question belong to a group that did decide on membership no sooner than 2150. The "say" in itself does not decrease the odds of Australia having been among the holdbacks.
So, in light of this definition, let's reword Crusher's comment. "What if one of the old nation states, say (suppose, assume, imagine, presume, hypothesize) Australia, had decided not to join the World Government in 2150?"
It is the same comment; nothing has changed.
Australia was a hypothetical choice, not one based on historical events.
Ah, but here comes the beef: it does not
matter whether Australia "really" joined or did not. This is irrelevant to the issue of whether Australia might have held back, or even to whether she did "in fact" hold back. Because the very fact that Australia was still in a position to make a choice as of 2150 is the decisive thing - from this we already learn that Australia must have been among the last to make the decision (which the wording unambiguously establishes as having been a "Yea, we'll join", of course).
That is why Australia qualifies for "possibly holding back".
It is after this that we move to step two and wonder whether making the choice at such a late date was exceptional or common, i.e. whether Australia (or any other random country out of Crusher's list) really influenced the issue in practice.
An alternate second step would be to surmise whether Crusher would choose a nation that in fact was on the verge of saying "Nay, we won't join", or a nation that definitely wasn't, or a completely random nation. If we knew Crusher well enough, we could home in on the psychologically most likely option of those three. But we don't.
I like this idea that the world government went into effect Jan. 1, 2150 at 12:00am GMT. All the nations that signed aboard the world government all became members at that time. Kinda like the 13 colonies were all states at the same time upon the Declaration of Independence. Australia, and the other nations, all may have voted months or years before to join and the treaty of new government simply didn't go into effect until 2150. Nice idea!
I rather like to think this is exactly how it must have happened, too - but this then directly means that the United Earth that apparently predated 2150 was not the World Government, not even a preliminary stage thereof. Which is fine and well, because we hear of UE (or at least UESPA) in the 21st century already, while the European Hegemony in the 22nd century, much later, was still credited as "the first stirrings" towards the World Government.
Timo Saloniemi