Australia is a country in Oceania comprising of the Australian continent and various smaller islands including Tasmania. The Wasteland is located in said country, and acts as the primary and sole setting of the Mad Max franchise.
History[]
It's likely that the history of Australia in Mad Max was the same—until the early 1980s(or the late 2010s in the reboot timeline)as that of real Australian history, from the inhabitance of First Nations peoples, to colonisation in the 18th century, followed by events such as the Commonwealth unification in 1901, Canberra being designated as the capital in 1911, the impacts of World War I and II, and more.
Mad Max[]
At some stage, however, just before the events of the first Mad Max film, there was a severe oil crisis and Australian society began to collapse. Fuel became scarce, looting became widespread, and law and order slowly began to disintegrate.
Apocalypse (or "Pox-eclipse")[]
At an unknown point in time, possibly either just before or after the events of Mad Max 2, a nuclear exchange that marked the end of oil-based civilisation broke out, causing a large number of casualties. It's likely that much of Australia was spared from the conflict, however, Sydney was hit and was shown to be abandoned in Mad Max: Beyond Thunderdome.