How were the borders of Indonesia set?

I was just reading about the quake in Indonesia, and looking at the map. And for the umptiumophth time, i wondered, how did that collection of islands and half islands become a single political entity.

The border with Malaysia always to be along mountain ridges, which makes a certain amount of sense. The border with Papua New Guinea is almost a straight line. Almost. And it looks like another island is cut up with a weird border.

I assume there are historical reasons for this. What are they?

As a rule of thumb, when looking at unusual borders, start with the assumption that it’s related to European imperialism. I don’t know a lot about that area, but Indonesia was controlled by the Dutch, while Malaysia was controlled by the British. Do the current borders relate to the respective areas of influence of those two imperial powers?

They are essentially the borders of the Dutch East Indies as they were at the end of WW2, and yes, they were the lines of border with the British Malay protectorates, the former German/Brit/Australian territories in Papua/New Guinea, and the remnant Portuguese colony in Timor. The Dutch proposed to create a federative style of organization of the different island groups after the war but the republican independence movement was succesful in taking over the entirety of the archipelago and suppressing what regional and insular states tried to assert themselves. Secessionist movements have continued to exist all along with varying degrees of intensity as time goes by.

The major border adjustments were that the Dutch held on to Irian (western New Guinea) until 1962, and that from 1975-2002 Indonesia occupied and tried to annex (the hard way) the former Portuguese colony in Timor L’Este but eventually had to recognize its independence.

Yes, the Indonesians several years after invading and occupying East Timor were persuaded to have a referendum because the international community did not believe it was the will of the occupied that they join Indonesia. The central government assumed they had done enough terrorizing, murder, displacement and replacement of occupants, and ballot stuffing to ensure they won the referendum to satisfy foreign observers,. They turned out to be wrong - the locals actually voted to regain their independence.

Papua New Guinea was apparently partly a German colony and partly a British colony. The Australians took over administration of both parts in WWI. The west half of the island was a Dutch colony, hence became part of Indonesia like the rest of the Dutch ex-colony that comprises Indonesia.

(Not unlike how Hispaniola is half Haiti, a former French colony, and the Dominican Republic, a former Spanish colony.)

Presumably all these colonies would start out as a settlement area in each isolated spot, then as they expanded or resources were found, the ruling colonial powers would take a pen and ruler to the map and say “OK, we’ll split it here” - presumably fairly distant to any existing settlements. If it was anything like Africa, what indigenous tribal areas or existing kingdoms were there was irrelevant.

There’s more to that than first meets the eye.


yes, the original agreement for the borders on Borneo was the catchment of the rivers… the watershed. This was left as an on paper border for decades… The Malay emergency ended with Indonesia agreeing that they wanted to be good neighbours, with certain encouragements paid/given.
(oil, war planes , those Sabres from Australia… )

After that they started to work with Malaysia to finally fix the borders with actual locations on the ground, rather than the vagaries of where water flows.

One island near Phillipines was in the 1898 Paris Agreement and its map as being handed over from Spain to USA … But this was erroneous as the dutch had already claimed it, settled it, etc, and anyway USA had left it vacant of any government ?? , probably the muslim residents wanted to be in the Dutch East Indies. …The USA didnt just agree to give it up, they took it to to a Swiss adjudicator who awarded it to Netherlands and hence its now part of Indonesia.

The borders on the island of Timor follow rivers. East Timor has a little exclave , which is the land of the Oecusse and Ambeno tribes. Some enterprising family had moved in and started up some farms for earning income and so on.

By the time the dutch were taking over the rest of the west part of the island, the mixed Portuguese Timorese people there had strong connections with Dili , and christianity and all things Portugese … and didn’t want to be taken over by the Dutch or islamists.

So anyway, the borders follow tribal boundaries, which are rivers.

There was also a period during which Indonesia was “confronting” Malaysia to try to absorb Northern Borneo.