Since Japan has no native source of oil, their oil reserved could only last for 2 years, and the US, Japan's major oil supplier, halted their oil shipments because of Japan's aggressive actions in China and Indochina, Indonesia, or should I say the Dutch East Indies, becomes a pivotal territory for the Japanese since the it was the fourth major source of oil in the world and was very rich on valuable materials such as rubber, which are very important for Japan to support further occupations of territories within Asia and the Pacific.
The Japanese invasion of the Dutch East Indies was codenamed 'Operation J', the invasion began on December 8, 1941 until the Japanese completely occupied the area on March 9, 1942. The Allies decided to skip retaking most of Indonesia and favored to retake the Philippines instead, to be able to isolate Japan from its major sources of materials within the Southeast Asia, (though they could just have invaded Formosa (Taiwan) if they wanted to save more time, lives and materials).
Japanese occupation of Indonesia ended upon Japan's surrender on August 15, 1945, then two days later, the Indonesians declared their own independence, but this wasn't recognized by the Netherlands that resulted to Indonesian National Revolution, after a series of fierce battles, eventually the Netherlands officially acknowledge Indonesia's independence on December 27, 1949. On 2005, the Netherlands accepted that Indonesia's independence day was indeed on the day of its declaration, which is August 17, 1945, making Indonesia as the first state in Southeast Asia to be fully decolonized.
