Why Japan Attacked Pearl Harbor

Part 3: The Second World War

The Japan government, meanwhile, was more and more controlled by the military. A national mobilization law gave the government absolute control over the nation's assets, and a 1940 act dissolved all political parties, replacing them with one authoritarian one. In the same year, Japan announced the existence of the Greater East Asia Co-Prosperity Sphere, with the aim of uniting Asian peoples under one banner–led by Japan, of course.

All of this took place against the backdrop of increasing tensions internationally. The response from other nations to Japan's invasion of Manchuria was outrage. As well, Britain and the U.S. actively supported China by sending food and supplies, through Burma and through other avenues.

The fall of France to Nazi Germany and Japan's military fortification of the Marshall Islands were two of the factors that convinced President Franklin D. Roosevelt to order the U.S. Pacific Fleet moved from California to Hawaii. This move would have been seen as provocative by the Japanese government.

In September 1940, after Japan had signed the Tripartite Pact with Germany and Italy and then seized French Indochina, the United States began an embargo on exports to Japan, stopping to that country shipments of steel, scrap iron, and aviation fuel. The Japanese war machine continued to get materials from elsewhere, however.

As Japanese conquests continued, more and more lands and water fell under the auspices of the Co-Prosperity Sphere. To shore up its northern border, Japan in April 1941 signed a neutrality pact with the Soviet Union. The absorption of Southeast Asia continued.

In August 1941, Great Britain, the Netherlands, and the United States froze Japanese assets in their respective countries. Up until that time, Japan had been able to count on monetary support in some form, even in the midst of the war. But the freezing of assets left Japan with very little in the way of currency, at a time when oil for the Japanese war machine was in short supply. German leader Adolf Hitler had promised oil as an incentive for Japan's attacking the Soviet Union, but Japan had refused. Later that year, the U.S. imposed an oil embargo on Japan.

The response from the Japanese government was to gain its oil and rubber (in limited amounts) from the nations it conquered and widen the war effort, while at the same time pursuing, through diplomatic means, the lifting of the oil embargo.

In October 1941, General Hideki Tojo was named prime minister. One of his actions was to set a deadline for waiting for a diplomatic resolution to the oil crisis. That date was November 25.

Part 4: Lead-up to the Attack

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