In the history textbook in Indonesian school, its been taught that Indonesia has been colonialized for 3.5 century by the Dutch.(a few years by the England, and Japan). But at that time, the Indonesian country isnt even formed yet, and the purpose of the Dutch journey is to trade(mostly). Although it slowly turned into a divide an conquer to the local monarchy. I just want some clarification about this part, some source would be appreciated.
Im sorry if this question has been asked before. If someone would kindly share the link, i would gladly delete the post.
This is a very good question, and one that is very difficult to answer in few paragraphs. Most history books use 1603 as the starting point of "Dutch colonization of Indonesia" or "VOC colonization of Indonesia". It is worth noting that the VOC were not the first of the Dutch to make it into Indonesia. The VOC was founded in 1602 in order to control and restrict both Dutch trade, and that of other competing nations, in Indonesia. The first is because several other expeditions had set off, many limped back laden with spices, and due to lack of regulation prior to 1602, the price of of spices fluctuated wildly, affecting profits and jeopardizing future expeditions.
So, the VOC started off as a monopoly company to regulate access, and thus prices, to their own advantage. In order for this monopoly to be effective, it had to be enforced both among the Dutch traders and against other competing powers, both European and "Indonesian".
The efforts of the VOC thus included many punitive raids and expeditions, including the infamous Amboyna massacre. While the VOC truthfully did tap into the local commerce networks, they had to compete against regional and European powers to control the trade networks they were profiting from.
Thus, on one hand, they did not indulge in outright colonial governance of all of Indonesia. This model was not common until the 19th century, when railroads and other technologies allowed European colonials to be able to even dream of directly ruling highly-populated territories in Asia and Africa. On the other hand, they ruthlessly kept control over their key assets, meaning ports, production facilities as appropriate, and of course sea lanes.
Because local powers could not freely trade nor interact with each other, let alone with other nations elsewhere, nor were they allowed to raise an army or navy, it is popularly accepted that they were considered to be "colonized".
The "divide and conquer" line that is often cited is a bit complicated to analyze because as you said, there was not yet an "Indonesia". Thus, it falls into the trap of historical determinism. So I prefer to analyze it on a case-by-case basis rather than as an abstract, poorly-contextualized concept.
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