Complex sentence: The PNG government made attempts to resolve the situation through June and July, but these failed, and the interim government announced that they would declare independence on 1 September, ahead of Papua New Guinea's own independence on 16 September.
Split into simpler sentences: The PNG government attempted to resolve the situation through June and July, but failed. The Interim Provincial Government announced that they would declare independence on 1 September, ahead of Papua New Guinea's own planned independence day of 16 September.