Institutional changes create a different alliance scenario

How would Australia and New Zealand react to a later Anglo-Japanese alliance?

Their response depends on whether they remain Dominions or share alliance decisions through a more integrated imperial federation.

A proposed later alliance adds more variables than the original wartime scenario can answer. Australia and New Zealand would have one kind of influence as Dominions and another inside an Imperial Federation or more integrated Commonwealth. Their place in the decision process changes whether the Anglo-Japanese alliance is imposed from London or collectively chosen. The constitutional structure assumed for the intervening decades determines the answer.