What are the three main groups that inhabit mainland of Papua New Guinea?

1. Austronesian people: These people make up the majority of the population of Papua New Guinea and are found in all parts of the country. They are believed to have migrated to Papua New Guinea from Southeast Asia around 3,000 years ago.

2. Papuan people: These people are found in the highlands and interior regions of Papua New Guinea. They are believed to be the original inhabitants of the country and are thought to have arrived sekitar 40,000 years ago.

3. Melanesian people: These people are found in the islands off the coast of New Guinea and on the smaller islands of the Bismarck Archipelago. The name "Melanesia" comes from the Greek words "melas," meaning black, and "nesos," meaning island, referring to the dark-skinned people of these territories.