Geography shaped history

South-Asia continental main waterways with commercial routes
South-Asia continental main waterways with commercial routes

Worldwide, until very recently when engineers were able to create bridges and later highways, communities and exchanges were concentrated in zones where water was readily available, so necessary for their successful development and life quality.
Great rivers, and their basins played a fundamental role in any civilization, but maybe never more than in monsoon-driven Oriental Asia, to feed the local populations and to permit permanent exchanges of people, merchandise, innovations and beliefs. To understand the deployment of the Bronze era of which drums constitutes one peak we must have a look at these early aquatic “highways” and their tributaries.
First, thanks to them rice progressively replaced wild resources and millet at the end of the Neolithic age and sedentary humans were able to mix the available ores to obtain bronze.
Second, let us imagine with arrows the continental water routes taken in the early days by traders of bronze items originating from the northern gulf of Bac Bo (Tonkin) to the gulf of Thailand and southern customers. At first they might join the Mekong, also easy to reach from the coast, and then cross the Khorat Plateau via the Mun River till not so far Chao Praya River down to the gulf of Thailand. From there, by coasting-trade or rivers via the Kra isthmus, the present Malaysia and then the straits of Indonesia were accessible.
Furthermore, when adequate compasses were invented, direct sea navigations in between northern and southern hubs could occur.
These main routes had probably been traveled for millennia and connections were already established between early chiefdoms, paving the way for a process of State(s) formation(s). For example, long before the drums, stone socketed axes or pottery with rouletted meander ornaments had been distributed via the same trails between Yunnan and (future) Thailand and Malaysia, connecting the continent to the southern Archipelagos.
Linguists distinguished in that large “bronze drums’ zone” at least two different basic type of languages and habits existence: Austroasiatic (from the continent) and Austronesian (from the islands), a distinction too complex to be more detailed here but fundamental to explain and relate the old interchanges to be explored along the way. In accordance different formats of skeletons and skulls in tombs including drums proved at least two cultural origins, either northern first based on Mon-Khmer ethnicities or southern with different “sub-tropical” peoples, with their respective specificities often seen in drum’s decorations.
In total a great puzzle, rich but complex to have in mind before to explore the zone.