In an effort to discourage Japanese militarism, Western powers including Australia, the United States, Britain, and the Dutch government in exile, which controlled the petroleum-rich Dutch East Indies, stopped selling iron ore, steel and oil to Japan, denying it the raw materials needed to continue its activities in China and French Indochina. In Japan, the government and nationalists viewed these embargos as acts of aggression; imported oil made up about 80% of domestic consumption, without which Japan's economy, let alone its military, would grind to a halt. The Japanese media, influenced by military propagandists,[29] began to refer to the embargoes as the "ABCD ("American-British-Chinese-Dutch") encirclement" or "ABCD line".
Faced with a choice between economic collapse and withdrawal from its recent conquests (with its attendant loss of face), the Japanese Imperial General Headquarters began planning for a war with the western powers in April or May 1941.
The key objective was for the Southern Expeditionary Army Group to seize economic resources under the control of the United Kingdom and the Netherlands, most notably those in Malaya and the Dutch East Indies, known as the "Southern Plan". It was also decided—because of the close relationship between the UK and United States, and the (mistaken)[30][31] belief the US would inevitably become involved[30]—Japan would also require an "eastern plan".
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