Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the world's sixth-largest country by total area. Neighboring countries include Indonesia, East Timor and Papua New Guinea to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. It is a member of the British Commonwealth, as well as a Major non-NATO ally of the United States, and has since supported the U.S. ever since.
The country was the first British settlement in the 18th century. Before that, it was inhabited by native Australians. The Dutch discovered the continent in 1606 while the British claimed the Eastern Half. It was only in 1901 where the six colonies united to form the Commonwealth of Australia. During World War II, General MacArthur barely escaped from the Philippines to Australia, and thus making it a hub for the allied forces in the Pacific. The Japanese also threatened invasion as well as bombing Darwin.
In the Homefront (series), the fate of Australia is not mentioned, alhtough it is assumed the country is facing invasion from the Greater Korean Republic due to it's proximity of the GKR occpuied/allied nations of Indonesia, East Timor and Papua New Guinea and due to its alliance with the United States. Despite that, the country seems to be free from Korean rule. It is probable that the Australian Defense Force and the New Zealand Defense Force have banded together in defending their coastline from the GKR, as well as having naval skirmishes with the KPA and helping the remnants of the US Navy reclaim American Overseas territories in the Pacific. Another probability is that some Americans may have taken refugee in these countries following the GKR's occupation of the Western United States.
Australia and New Zealand may send aid to U.S. along with the European Union, but this all subject to speculation.