Trade: Jade and goods from Sahul

`

In those days Sundaland was a centre for commerce thanks to an abundance of commodities and skilled craftsmen. A thousand ships set out from the harbours of the cities powered by oar and sail to bring hard woods, animal hides, metal ore, jewellery and more to any that could afford them. They sailed up the East coast even as far as the land of the Yellow river and returned with jade, precious metals and stones, soft fabrics and exotic animals. A network of commerce spread through the hinterlands through the rivers and roads and many people benefitted from increased demand and industry. 

- An Account of Sundaland by Alom Takal 

No setting is complete without considering what kinds of commodities are traded between cultures. It seems there is a long history of trade in Jade from Taiwan down the coast (it was more valuable than gold and silver in ancient China) so that creates a good reason for sea based trading routes to exist along the East side of Sundaland in our setting.

Perhaps there are pirates lying in wait amongst the thousands of islands of what we now call the Philippines and Sulawesi? Perhaps there are kingdoms and city-states on those islands that extract a tax in exchange for escorts and safe passage? They might also be hubs of trade for commodities from Sahul (the ancient Australia - Papua New Guinea continent) which has been split from Asia for so long (50 million years) that it developed a very different ecosystem.

For example Eucalyptus (Wikipedia: Eucalyptus cultivation and uses) trees are not found on the Asian side of the line, neither are Marsupials and Monotremes. All of these might be of interest to traders.

Wikipedia: Jade in Southeast Asia
Wikipedia: Sahul Shelf
Wikipedia: Wallace Line