How did Papua New Guinea become an independent country?

Papua New Guinea's road to independence is quite complicated.

The northern half of Papua New Guinea was known as German New Guinea after it came under German control in 1884, while the southern half was known as British New Guinea, later renamed to Papua in 1904. During WWI, the island was occupied by Australian troops to defend the British half. When the Treaty of Versailles was established after World War I, Australia administered German New Guinea, and the British part of the island came to be considered an External Territory of the Commonwealth of Australia, though it was still "owned" by Britain. The two territories were regarded as separate territories, known as 'Papua' and 'New Guinea'.

After the New Guinea Campaign of World War II, the two territories came together as 'Papua New Guinea'. Australia still administered Papua New Guinea until the country was granted full independence on 16 September 1975. Papua New Guinea's Head of State is still the Queen of England, just as Australia's is, as it remains a member of the Commonwealth of Nations.