Australia (/əˈstreɪljə/), officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. 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, Vanuatu, and New Caledonia to the north-east; and New Zealand to the south-east.For at least 40,000 years before European settlement in the late 18th century, Australia was inhabited by indigenous Australians, who belonged to one or more of roughly 250 language groups. After discovery by Dutch explorers in 1606, Australia's eastern half was claimed by Great Britain in 1770 and settled through penal transportation to the colony of New South Wales from 26 January 1788. The population grew steadily in subsequent decades; the continent was explored and an additional five self-governing Crown Colonies were established.On 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Since Federation, Australia has maintained a stable liberal democratic political system which functions as a federal parliamentary democracy and constitutional monarchy. The federation comprises six states and several territories. The population of 22.7 million is heavily concentrated in the Eastern states and is highly urbanized. A highly developed country, Australia is the world's thirteenth largest economy and has the world's seventh-highest per capita income. Australia's military expenditure is the world's twelfth largest. With the second-highest human development index globally, Australia ranks highly in many international comparisons of national performance, such as quality of life, health, education, economic freedom, and the protection of civil liberties and political rights. Australia is a member of the G20, OECD, WTO, APEC, UN, Commonwealth of Nations, ANZUS, and the Pacific Islands Forum.