What was the only war in which Australia was invaded?

World War 2, was the only war where Australia was invaded

WW2.

Explanation:

The japanese invaded the port city of darwin with an air raid.  

another technical "war" was the australian war on Emus.  The emu population was growing too rapidly so many australians were forced to fight back.  The war was not successful and the Emu population is still too large