The Road to Pearl Harbor: The United States and East Asia, 1915–1941

Although most Americans were shocked by the Japanese attack on Pearl Harbor on December 7, 1941, the outbreak of war between the two countries came as no surprise to most observers of international affairs. Indeed, the war could be seen as the culmination of tensions between the two countries that can be traced back to 1915, when Japan issued its so-called "Twenty-One Demands" on China. These demands, presented as an ultimatum to the Chinese government, would have amounted to giving Japan a privileged status in certain parts of the country. This was in direct conflict with the stated policy of the United States toward China—the famous "Open Door," in which all countries were to respect Chinese sovereignty and enjoy equal access to Chinese trade.

Exacerbating the situation were the economic problems of Japan in the late 1920s, made worse by the Great Depression which swept the industrialized world in the early 1930s. As an island country with few natural resources, Japan was dependent on international trade, which was disrupted by the economic crisis. Moreover, Japan was overpopulated, but other countries—most importantly the United States—closed the door to Japanese emigrants. Increasingly Japan's military leaders became convinced that only through domination of China could they solve their country's problems. Japan's excess population could be settled in the largely undeveloped Chinese province of Manchuria, while Japanese industry could be revitalized through control of China's import market.

Therefore the 1930s saw a steadily increasing campaign of Japanese aggression in China, beginning with the invasion of Manchuria in 1931 and culminating in the outbreak of full-scale war between the two powers in 1937. Each instance of aggression resulted in denunciations from the United States, but the administrations of the time—that of Herbert Hoover until 1933, and of Franklin D. Roosevelt thereafter-understood that there was no will on the part of the American public to fight a war in East Asia. Therefore U.S. policy by the late 1930s consisted of nothing more than a refusal to recognize Japanese conquests, limited economic sanctions against Japan, and equally limited military and economic assistance for China.

Nevertheless, the Japanese bitterly resented even these halfway measures, and when their war against China bogged down in 1939 they blamed outside interference for the stubborn refusal of the Chinese to submit to their terms. They sought a way to prevent foreign aid from reaching China, and to replace the foreign resources that they could no longer acquire due to American economic sanctions.

In Germany's lightning victories of April–June 1940 Tokyo believed it had found the answer to both problems. In Southeast Asia and the South Pacific lay a number of territories controlled by France, the Netherlands, and Great Britain, which none of those countries appeared capable of defending. If they were to fall into Japanese hands Tokyo's strategic dilemma, it seemed, could be solved. After concluding an alliance with Germany in July 1940, Japan pressured the French government into allowing Japanese troops to occupy the northern part of French Indochina. In the following year Japanese forces occupied the entire country.

The U.S. government met this latest series of aggressive moves with a steadily escalating campaign of economic sanctions, so that by late summer of 1941 Japan was no longer able to purchase any materials from the United States. This was a tremendous blow for many reasons, but particularly because Japan was almost completely dependent upon U.S. imports for its supply of oil. Without oil, of course, Tokyo would have to abandon its war against China—a humiliation that no Japanese leader would accept.

The result was a frenzy of diplomatic maneuvering between Japan and the United States throughout the second half of 1941. However, Tokyo knew that time was running out; if the United States failed to drop its trade sanctions Japan would run out of oil within months. Therefore Japan's leaders made a fateful decision-if no settlement could be reached with Washington by the end of November there would be war. Moreover, the Japanese naval command concluded that this war must begin with the most devastating attack possible against the United States—an air strike, using carrier-based planes, against the U.S. Pacific Fleet at Pearl Harbor. The result, of course, would be a four-year conflict that, in the end, would prove disastrous for Japan.