The challenge is to give the island of New Guinea (north of Australia) a white/non-native majority.
Ive just started wondering why European colonisation of Australia and New Zealand was successful in establishing European-majority countries but a relatively similar island in the same area was not. After all it was ruled by three European empires over its history (British/Australian, German, Dutch) so why was there no emigration there.
Bonus points if you can unite the island into one county too, and try do it with no genocide and equal rights among the ethnic groups.
POD can be anytime (most likely to be pre-1900 though), and the white majority should be achieved before the 21st century.
Good luck