• 1937

    Japan goes to war with China

  • July1939

    Roosevelt announces that Treaty of Commerce and Navigation will not be renewed

  • July2, 1940

    U.S. Congress passes Export Control Act

  • August

    Japan declares greater East Asia co-prosperity sphere

  • September27

    Japan signs Tripartite Pact with Germany and Italy

  • January1941

    Yamamoto prepares plan for attack on Pearl Harbor

  • July

    Japanese troops occupy Indochina

  • October

    Hirohito gives general approval for Pearl Harbor attack

  • November8

    Hirohito approves formal battle plan for attack in December

  • November26

    Japanese attack fleet sets sail from Japan

  • December7

    Japan launches surprise attack on Pearl Harbor

  • December8

    United States and Britain declare war on Japan

  • December11

    Germany declares war on United States

    • Key People

    • Franklin D. Roosevelt

      32nd U.S. president; implemented economic penalties that angered Japan; requested war declaration after Japanese attacked Pearl Harbor in December 1941

    • Yamamoto Isoroku

      Japanese admiral who planned surprise attack at Pearl Harbor

    • Hirohito

      Japanese emperor; approved Pearl Harbor attack plan

    • Richmond K. Turner

      U.S. Navy admiral; warned that navy be put on high alert status and security increased at Pearl Harbor, but recommendations were implemented only partly

    Tensions in the Pacific

    In the years prior to the outbreak of World War II in Europe, tensions were also escalating in the Pacific region. Japan, which had been at war with China since 1937, had declared openly its intent to take over as much of eastern Asia as it could. It also had serious ambitions toward taking territory in the Soviet Union. If Germany, which the Japanese government saw as a potential ally, would attack Russia from the west, Japanese military leaders felt that they stood a good chance of seizing Soviet-controlled territory in the east. The signing of the German-Soviet Nonaggression Pact in 1939 therefore caused a huge scandal in Japan, as it directly undermined Japan’s plans.

    Japan and the United States

    In the meantime, the United States was becoming more and more of a problem for Japan. Throughout the 1930s, the United States and many European nations, suffering from the Great Depression, enacted high protective tariffs. These tariffs greatly curbed Japanese exports and heightened the effects of their own economic depression. The poor economic conditions caused strong anti-Western sentiment in Japan and were a strong factor in forcing the Japanese invasion of China.

    In July 1939, President Franklin D. Roosevelt decided not to renew the 1911 U.S.-Japan Treaty of Commerce and Navigation, which was due to expire in January 1940. Then, on July 2, 1940, the U.S. Congress passed the Export Control Act. Together, these two actions effectively eliminated Japan’s primary source of oil, scrap metal, and other material resources needed for war.

    These developments dealt not only a severe economic blow to Japan but also a humiliating slap in the face to Japan’s leaders, who felt that the United States had no right to pass judgment on them or to interfere in their affairs. Although Japan was still smarting from the German-Soviet Nonaggression Pact, the United States’ actions were enough to overcome this resentment, and on September 27, 1940, Japan signed the Tripartite Pact with Germany and Italy. The pact made the three nations official allies.

    The United States Prepares for War

    Although the United States remained officially neutral during the first two years of World War II, the Roosevelt administration was far from indifferent or oblivious to the conflict. The United States provided material support first to Britain and later to the Soviet Union, secretly at first but then with increasing openness over time. Chief among these measures was the March 1941Lend-Lease Act,which empowered Roosevelt to give aid to the Allies in exchange for whatever kind of compensation or benefit the president deemed acceptable. The American people also paid close attention to the events developing in the Pacific and, by mid-1941, considered war with both Japan and Germany to be likely possibilities.

    U.S. intelligence services had direct access to Japanese coded transmissions, so U.S. officials were well aware that the Japanese were planning something against them—they just did not know precisely what. One man in particular, Admiral Richmond K. Turner, strongly urged that U.S. forces be placed on a higher state of alert, as he was particularly concerned about the U.S. Navy base at Pearl Harbor, Hawaii. During previous U.S. war games and exercises, Pearl Harbor had proven highly vulnerable to surprise attacks. Although Turner’s advice was considered, only some of his recommendations were implemented.

    Popular pages: World War II (1939–1945)