Prior to 1945, Indonesia was a colony of the Netherlands. When Japan began to expand, Japanese leaders decided to support an independence movement in Indonesia to drive the Netherlands out of its sphere of influence.
Achmed Sukarno and Muhammad Hatta collaborated with the Japanese military to reclaim Indonesia from the Dutch government. When Japan surrendered to the United States in 1945, Sukarno and Hatta feared that their window of opportunity was closing.
On 17 August 1945, Sukarno announced the Proclamation of Indonesian Independence. In Indonesian, the proclamation is known as Proklamasi Kerdekaan Indonesia. Soon after the announcement of the proclamation, Sukarno and Hatta used Japanese weapons and equipment to revolt against the Dutch government in Indonesia.
The Dutch were initially driven out of Jakarta, but reinforcements ensured that fighting would continue until 1949. Weary of bloodshed, the United Nations blocked the Netherlands’ ambitions to go to war by calling for diplomatic measures. After ten weeks of tedious debates, Indonesia was granted its independence and Dutch forces withdrew from East Asia. In August 1949, the United States of Indonesia was founded.
Description by Indonesian Public Holidays