hi! there's a section in the FAQ* on this, although it focuses on American accents ~
as for Australian (and others), here are some more:
How did American and Australian accents develop into their modern forms from their British origins?
Why do Oceanian accents sound closer to British than North American ones?
How did the Australian accent become so differentiated from a typical English accent?
Is the American and Canadian accent the original British accent?
*see the link on the sidebar or the wiki tab