The Second Sino-Japanese War had seen tensions rise between Imperial Japan and the United States; events such as the Panay incident and the Nanking Massacre turned American public opinion against Japan. With the occupation of French Indochina in the years of 1940/41 and the continuing war in China, the United States embargoed strategic materials such as scrap metal and oil to Japan, which were vitally needed for their war effort. The Japanese were faced with the option of either withdrawing from China and losing face or seizing and securing new sources of raw materials in the resource rich, European controlled colonies of South East Asia ? specifically British Malaya and the Dutch East Indies (modern-day Indonesia).

On September 27, 1940, Imperial Japan signed the Tripartite Pact with Nazi Germany and Fascist Italy, their objectives to "establish and maintain a new order of things" in their respective world regions and spheres of influence; with Nazi Germany in Europe, Imperial Japan in Asia and Fascist Italy in North Africa. The signatories of this alliance become known as the Axis Powers. The pact also called for mutual protection?if any one of the member powers was attacked by a country not already at war, excluding the Soviet Union, and for technological and economic cooperation between the signatories.

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