High Quality Content by WIKIPEDIA articles! Australia entered World War II shortly after the invasion of Poland, declaring war on Germany on 3 September 1939. By the end of the war, almost a million Australians had served in the armed forces, whose military units fought primarily in the European theatre, North African campaign, and the South West Pacific theatre. In addition, Australia came under direct attack for the first time in its history; its casualties from enemy action during the war were 27,073 killed and 23,477 wounded.