Well with the arts Dean's scholar you had to do an interview and resume. They have already started telling people if they are on the acceptance list for this course with arts, not sure bout commerce.
Err te dot point is the effect of war on the home fronts of Japan, Australia and the U.S., so technically its all three. BUT they usually ask the question like blah blah discuss Japan and either Australia or the US, so you can kinda get away with only knowing two really well.
The problem with decolonisation is that the syllabus only says you need to know an overview of it, therefore they aren't likely to ask a whole question just on that. They would combine it with another key feature or timeline event etc.