Indonesia seems to have an interesting dichotomy (or at least division) between coastal and inland settlements. Both types of settlements seem to have similar levels of power, but they exercise them in different ways (according to some scholars). Inland sites generally produce or collect goods that can be traded and send them to the coastal sites. Coastal sites were the main trade centres, so they exchanged the goods form inland to merchants for foreign goods and controlled the distribution of those goods to inland sites.
But here’s what’s interesting. The inland sites in Indonesia seem to be fairly mobile, partly due to availablity of resources, but also due to their relationship with the coastal sites. If a coastal site decided to pay an inland site lower than they felt their goods deserved, the inland site would simply move and trade with a different coastal site, thereby destroying a large part of the coastal site’s economy. There was nothing inherently connecting them to a coastal site (according to some scholars), and so they could sell to the highest bidder. So the inland suppliers had a degree of power over the coastal sites, just as the coastal sites held power over the inland sites in terms of the flow and control of foreign goods.
There is an argument for landscape causing the formation of this relationship: that the inland settlements didn’t have access to good agricultural land because it was all swampy floodplain or steep mountains and the monsoons were unreliable, and that the coastal settlements didn’t have much access to agricultural land because they were on the coasts and the soils were relatively poor.
There are several things that people are saying. 1) The natural environment and available agricultural land of Southeast Asia caused people to settle in various places, namely the coast and inland, but neither region has fantastic access to arable land, 2) there is a dichotomy between coastal and inland settlements, and 3) this dichotomy caused both types of settlements to become political powers within the region. Given these three statements, we could argue that the heterarchy we see in prehistoric and early historic Southeast Asia might be, at least in part, caused by the environmental factors of the region. We could be seeing similar cultural adaptations to the common problem of lack of arable land. Because they didn’t have suitable agricultural prospects, these groups turned to exchange to get the goods needed to run their society.
Not a definitive thing, but cultural adaptation to environmental factors is certainly something to consider when looking at difference in Southeast Asian societies and the differences between them (along with, honestly, a whole host of other factors).