from the Tips and notes for the skill Accusative:
The -n ending in Esperanto is called the accusative.
Be aware that the accusative ending -n is never used with the verb estas:
Li estas knabo. (He is a boy.)
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There is a country called Australia, or the Commonwealth of Australia, which almost exactly corresponds to a landmass that can be termed mainland Australia, plus the island of Tasmania.
It sits on a continent that is variously described as Australia, Australasia, or Oceania, which comprises the Australian landmass plus some of the surrounding islands such as New Zealand and New Guinea.
Australians live in Australia.
Aŭstralianoj loĝas en Aŭstralio.
(Aŭstrali'an'o'j loĝ'as en Aŭstrali'o.)
Your assumption - that Australia is a "new world" country - is correct,
but you got tricked (or rather: missed an -i- ) on the "what's the root word?" part ...
(the root is Aŭstrali' (see la Plena Ilustrita Vortaro de Esperanto)