The history of the Australian American population almost follows the story of both British Americans and Irish Americans, as Australia was a British political territory at the time when they first emigrated and most of the settlers were Irish. The first wave of emigration from Australia to the United States came in the 1850s California Gold Rush when mostly Irish migrants who had escaped the Great Irish Famine had previously worked on the Australian goldfields. In San Francisco, the "Sydney Ducks" as they were known, were in violent conflict with nativist locals. Transpacific immigration then dried up while the American Civil War waged. It picked up during the period of Reconstruction, but faltered again when Australia was hit by a depression in the late 1890s. Immigration to the United States peaked in the years following World War II, due to America's increased economic activity, and the exodus of 15,000 Australian war brides who married U.S. servicemen. From 1971 to 1990, more than 86,400 Australians and New Zealanders immigrated to the United States.
At the 2000 U.S. Census, 60,965 Australian born people were enumerated in the United States, of which 15,315 were citizens. Around 40% of Australian Americans had entered the United States before 1980. Australians speak more than 260 languages and identify with over 270 ancestries. Following World War II, the first waves of migrants and refugees to Australia came mostly from Europe, diversifying what was then a mostly Anglo-Celtic nation. Later waves have come from the Asia–Pacific region, the Middle East and Africa, contributing to the diverse population that exists today. Aboriginal and Torres Strait Islander people remain a further source of Australia's varied backgrounds.