Why did England think Australia as terra nullius?

Answer 1

Terra Nullius means "land that belongs to no-one".

England thought of Australia as terra nullius because the British did not recognise that the indigenous people of Australia were the rightful "owners" of the land. Because the Aborigines were seen as little more than black savages, the British considered that Australia belonged to no-one and that it was within their right to claim the land as their own, and to do with it (and its people) whatever they wished.