They're basically the proto Pacific Islanders. It's believed that their civilizations all trace back to a group of people from the island of Taiwan/Formosa, who learned how to sail over the deep ocean and set up new communities, bringing chickens, pigs, taro, coconuts.

They settled modern day Indonesia, Malaysia, the Philippines, as far west as Madagascar, to Melanesia, Micronesia, and Polynesia, and most of the other Pacific Islands, as far east as Easter Island. Native Hawaiians, Samoans, Guamese, etc., are all Austronesian. Most ethnic groups considered native to these islands trace back to Austronesian expansion.

There are shared linguistic and cultural ties that showed that they had recent comment ancestry, that has since been confirmed by DNA genealogy.