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Since we already looked at fascism, why not look at the other end of the spectrum also. Australia is a country that historically has had a pretty strong union movement, so what could trigger an event that could lead to either communists being elected or a communist revolution.

Also assume that their is no real British intervention (due to either a) not wanting to risk a war b) needing potential allies c) overall not being bothered).

Make Australia a communist country post WW1.
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