As the dominant power in Asia, Japan had long resented that the United States, Great Britain, France, Portugal, and the Netherlands controlled parts of the Asian mainland and the Pacific. It wanted to replace these colonial powers with its own Greater East Asia Co‐Prosperity Sphere
and was prepared to use force to achieve this goal. Japan followed up the occupation of Manchuria with the bombing of Shanghai in 1932 and began a full‐scale war in China in 1937. Japan's action in China led to an informal American boycott of Japanese goods as well as a major building program that would prepare the U.S. Navy to fight in both the Atlantic and Pacific. By 1940, Japan was planning to extend its control to the natural‐resource‐rich French colonies in southeast Asia and the Dutch East Indies.
Growing tensions with the United States. During the summer of 1940, the collaborationist Vichy government in France gave the Japanese military access to Indochina (Vietnam, Laos, and Cambodia). In September, Japan formally joined the Axis by signing the Tripartite Pact with Germany and Italy. The treaty committed the signatories to declare war on any nation that attacked one of them. By the time the mutual assistance pact was signed, the United States had already announced restrictions on exports of aviation fuel and scrap metal to the Japanese. With the exception of coal, Japan was heavily dependent on other countries for raw materials, and the United States hoped to exploit this weakness through economic sanctions. Negotiations during the spring of 1941 to resolve outstanding differences were ineffective, however.
By July 1941, the Japanese occupied all of French Indochina in a prelude to invading the Dutch East Indies, an important source of oil and rubber. Roosevelt froze all Japanese assets in the United States, bringing an end to trade between the two countries. Although Japanese leaders approved an attack against American forces in the Pacific as early as September, talks continued and Japan presented a formal proposal for a peaceful settlement to Secretary of State Cordell Hull on November 20. In the proposal, Japan agreed to cease its southern expansion if the United States would cut off aid to China, restore trade, and help secure access to supplies that Japanese industry needed from the Dutch East Indies. This was not a serious offer. The party supporting war had already taken over the Japanese government in October when General Hideki Tojo became prime minister. As Tojo expected, the United States rejected the proposal and instead called for Japan to immediately withdraw from Indochina and China. On the same day (November 26), a task force of Japanese carriers left for Pearl Harbor.
The attack on Pearl Harbor. American cryptographers had broken the Japanese diplomatic code and knew that an attack was imminent by the end of November. Even though the War and Navy Departments believed that the most likely targets were either the Philippines or southeast Asia, they issued warnings to all U.S. commanders in the Pacific. At Hickham Field in Hawaii, General Walter Short was more concerned about sabotage than an air attack and placed his planes wing tip to wing tip to make it easier for the sentries to patrol. His decision proved disastrous when Japanese planes dropped their bombs on the morning of December 7, 1941.
Japanese military planners realized they could not win a protracted war with the United States. They pinned their hopes on quickly knocking out the U.S. Navy with a single blow against Pearl Harbor on Oahu, Hawaii, the home base of the Pacific fleet. The air attack was the costliest naval defeat in American history — 19 ships were either sunk or severely damaged (including 3 battleships), about 150 planes were lost, and more than 2,300 soldiers and sailors were killed. But the attack failed in two important respects. The destruction of the fleet was not as complete as the Japanese had planned; the three American aircraft carriers stationed at Pearl Harbor were on maneuvers and were not in port on December 7. Moreover, the oil depots were not bombed. Their loss would have forced the surviving ships to return to the mainland for refueling.
The Japanese government had intended to present its final message breaking off negotiations with the United States to the State Department before the air attack began, but the message was delivered an hour late. When the Japanese envoys (who were unaware that the war had already started) met with Hull, the secretary scathingly told them what their country had done. In addition to Pearl Harbor, Japanese forces were also attacking the Philippines, Guam, and Midway Island, as well as the British in Hong Kong and Malaysia on December 7, in a coordinated strike across the Pacific. Roosevelt asked Congress for a formal declaration of war against the Empire of Japan on December 8, 1941. Representative Jeannette Rankin of Montana, who had also voted against war in 1917, cast the only dissenting vote. Three days later (December 11), Germany and Italy declared war on the United States. The war in Europe and the war in Asia had merged into a global conflict.