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. For at least 40,000 years before European colonization in the late 18th century, Australia was inhabited by indigenous people who belonged to one or more of roughly 250 language groups. Traditionally most indigenous Australians were hunter-gatherers, with a complex oral culture and spiritual values based on reverence for the land and a belief in the Dreamtime. The indigenous population, estimated at 750,000 to 1,000,000 at the time of European colonization, rapidly declined as a result of disease, government policies, destruction of traditional lifeways, and other actions. Today, the indigenous people of Australia – commonly referred to as Aboriginal and Torres Strait Islanders – comprise 2.3% of the total population. Like their indigenous brothers and sisters, they face a number of common struggles: sovereignty, the right to self-determination, preservation of language and heritage, rights to land and natural resources, impacts from climate change and environmental damage, and recognition within local, federal, and international governments and laws.