The eastern half of the island of New Guinea — second largest in the world — was divided between Germany (north) and the UK (south) in 1885.
The latter area was transferred to Australia in 1902, which occupied the northern portion during World War I and continued to administer the combined areas until independence in 1975.
A nine-year secessionist revolt on the island of Bougainville ended in 1997 after claiming some 20,000 lives.