Indonesian nationalism and movements supporting independence from Dutch colonialism, such as Budi Utomo, the Indonesian National Party (PNI), Sarekat Islam, and the Indonesian Communist Party (PKI), grew rapidly in the first half of the twentieth century. Budi Utomo, Sarekat Islam and others pursued strategies of co-operation by joining the Dutch initiated Volksraad ("People's Council") in the hope that Indonesia would be granted self-rule. Others chose a non-cooperative strategy demanding the freedom of self-government from the Dutch East Indies colony. The most notable of these leaders were Sukarno and Mohammad Hatta, two students and nationalist leaders who had benefited from the educational reforms of the Dutch Ethical Policy.
The occupation of Indonesia by Japan for three and a half years during World War II was a crucial factor in the subsequent revolution. The Netherlands, under German occupation, had little ability to defend its colony against the Japanese army, and within only three months of their initial attacks, the Japanese had occupied the Dutch East Indies. In Java, and to a lesser extent in Sumatra (Indonesia's two dominant islands), the Japanese spread and encouraged nationalist sentiment. Although this was done more for Japanese political advantage than from altruistic support of Indonesian independence, this support created new Indonesian institutions (including local neighbourhood organisations) and elevated political leaders such as Sukarno. Just as significantly for the subsequent revolution, the Japanese destroyed and replaced much of the Dutch-created economic, administrative, and political infrastructure.
Under pressure from radical and politicised pemuda ('youth') groups, Sukarno and Hatta proclaimed Indonesian independence, on 17 August 1945, two days after the Japanese Emperor’s surrender in the Pacific. The following day, the Central Indonesian National Committee (KINP) elected Sukarno as President, and Hatta as Vice President.
Euphoria of revolution
We, the people of Indonesia, hereby declare the independence of Indonesia.
Matters which concern the transfer of power and other things will be executed by careful means and in the shortest possible time.
Djakarta, 17 August 1945
In the name of the people of Indonesia,
(Translation by the Ministry of Foreign Affairs, October 1948)
Bendera Pusaka, the first Indonesian flag, is raised on 17 August 1945.
It was mid-September before news of the declaration of independence spread to the outer islands, and many Indonesians far from the capital Jakarta did not believe it. As the news spread, most Indonesians came to regard themselves as pro-Republican, and a mood of revolution swept across the country. External power had shifted; it would be weeks before Allied Forces entered Indonesia, and the Dutch were too weakened by World War II. The Japanese, on the other hand, were required by the terms of the surrender to both lay down their arms and maintain order; a contradiction that some resolved by handing weapons to Japanese-trained Indonesians.
The resulting power vacuums in the weeks following the Japanese surrender, created an atmosphere of uncertainty, but also one of opportunity for the Republicans. Many pemuda joined pro-Republic struggle groups (badan perjuangan). The most disciplined were soldiers from the Japanese-formed but disbanded Giyugun (PETA) and Heiho groups. Many groups were undisciplined, due to both the circumstances of their formation and what they perceived as revolutionary spirit. In the first weeks, Japanese troops often withdrew from urban areas to avoid confrontations.
By September 1945, control of major infrastructure installations, including railway stations and trams in Java's largest cities, had been taken over by Republican pemuda who encountered little Japanese resistance. To spread the revolutionary message, pemuda set up their own radio stations and newspapers, and graffiti proclaimed the nationalist sentiment. On most islands, struggle committees and militia were set up.Republican newspapers and journals were common in Jakarta, Yogyakarta, and Surakarta, which fostered a generation of writers known as angkatan 45 ('generation of 45') many of whom believed their work could be part of the revolution.
Republican leaders struggled to come to terms with popular sentiment; some wanted passionate armed struggle; others a more reasoned approach. Some leaders, such as the leftist Tan Malaka, spread the idea that this was a revolutionary struggle to be led and won by the Indonesian pemuda. Sukarno and Hatta, in contrast, were more interested in planning out a government and institutions to achieve independence through diplomacy. Pro-revolution demonstrations took place in large cities, including one led by Tan Malaka in Jakarta with over 200,000 people, which Sukarno and Hatta, fearing violence, successfully quelled.