The presence of Indonesia Communist Party (PKI) brings a lot of difference in revolution progress. The radical youth who fight among the Dutch colonizers—assembling under the same roof—PKI, who supports the lives of proletarians in Indonesia, same as other communist principles.
Many ideas were united, many people exchanged their ideas for the independence of their beloved homeland—Indonesia. The colonial government that was aware of the PKI presence, captured and disposed of important people from it. However, they still can maneuver the party from afar. Sending letters to each member to keep every idea and principle alive.
Around the 1920s, they failed to do a mass action. Their party is strong enough from the scale of members—but not strong enough from the whole national scale. They didn't have enough support from the proletarians that time. If they did, it only lasted 2-3 months—the mass action didn't spread to the whole Indonesia.
Yet, the same thing happened in 1948. Four years after Indonesia's independence, ex-prime minister Amir Sjarifuddin and his cabinet made an agreement with the Dutch colonial in a warship transport—USS Renville. The result of the agreement were:
The Dutch acknowledge Central Java, Yogyakarta, and Sumatra as a part of the Republic of Indonesia.
Approval of the demarcation line that separates part of Indonesia territory and Dutch territory.
TNI (Indonesian National Army) should pull back its enclaves in the occupied territories.
Many people were disappointed with the result as they thought it could harm Indonesia—decreasing the territory of Indonesia. Regions that produce basic needs were controlled by the Dutch. The Renville Agreement also eliminated the position of the left movement in Indonesia—soon would be the beginning of rebellion from the left-wing people that got reorganized as FDR (Front Demokrasi Rakyat) which consists Socialist Party, PKI, PBI, Pesindo, and federation of trade unions SOBSI.
Here is the plot twist! The ex-prime minister Amir Sjarifuddin was the one who found FDR. There could be a chance Amir himself was disappointed in the result of the Renville Agreement he and his people had agreed to.
FDR gradually entered the opposition. Its opposition to several "peaceful" paths achieving peace with the Dutch colonial. Around September 18, the rebellion happened. Musso, one of PKI leaders, proclaimed the Soviet Republic of Indonesia—opposed and declared war on the government of the Republic of Indonesia.