main idea of this book is to explain the author's concepts of the Nusantao and the Nusantao Martitime Trading and Communication Network. which is, according to wiki:

http://en.wikipedia.org/wiki/Nusantao_Maritime_Trading_and_Communication_Network

The Nusantao Maritime Trading and Communication Network (NMTCN) is a trade and communication network that first appeared in the Asia-Pacific region during its Neolithic age. Wilhelm Solheim first suggested the concept in 1964. The NMTCN attempts to explain the diffusion of cultural traits throughout the Asia-Pacific region, a pattern that does not seem to match the projections of cultural spread by simple migration theories. Today, it is one of the dominant theories for the early peopling of the Southeast Asian region.

Solheim suggests that "[if] elements of culture were spread by migrations, then the spread would have been primarily in one direction." He suggests that since the pattern of cultural diffusion in the Asia-Pacific region is spread in all directions, it is likely that the spread of cultural traits happened via some kind of trading network, rather than a series of migrations.

In Solheim's hypothesis, the people who constituted this trading network are referred to as "the Nusantao".