Why Japan Attacked Pearl Harbor

Part 4: Lead-up to the Attack

Tojo and his government, in concert with the rest of the military, devised a plan for widening the war. The plan called for a wide net of operations for a December 1941 invasion, into Burma and the East Indies and Malaya and the Philippines. The first three elements on that list belonged to European powers, most notably Great Britain. The Philippines was another matter.

Spain had controlled the Philippines for many years before the American victory in the Spanish-American War. The U.S. played a large role in the running of the Philippines until 1934, when a limited form of independence was declared. The plan was for the country to become fully independent in 1944. Roosevelt had also sent General Douglas MacArthur to the Philippines to oversee the training of that country's military. Thus, Japan's leaders expected a military response from the U.S. to a Japanese invasion of the Philippines.

That military response would naturally come, in large part, from the naval base at Pearl Harbor, in Hawaii. The Pacific Fleet had been based there since June 1940. But the naval strength of the U.S. Navy in late 1941 was not what it once was. The combination of the Great Depression and an isolation policy pursued by the U.S. Government during the 1920s and early 1930s had left relatively little money for some much-needed upgrades to American elements of war. And the architect of Japan's attack on Pearl Harbor, Admiral Isoroku Yamamoto, knew this because he had spent considerable time in the U.S., as a student at Harvard University and as a naval attaché in Washington, D.C.

Japan had other reasons to include in its December invasion plans a surprise attack on the the U.S. Pacific Fleet. Germany had invaded the Soviet Union in June 1941, and German gains against Soviet positions were significant. The Japanese government judged the threat of a Soviet revocation of its nonaggression treaty with Japan very small. As well, American efforts at this time were primarily in the form of support for Allied nations fighting in Europe and that aid had not been immediate in coming.

The Japanese secret deadline for a diplomatic resolution came and went. Yamamoto warned that an attack on the U.S. would be successful at first but that America would eventually recover.

Many in the Japanese military thought that the devastation of the U.S. Pacific Fleet would cripple the American Pacific war effort so much that a response would be too little, too late. Others in the Japanese military thought that the response from America would be to sue for peace.

Neither of those was the result of the attack on Pearl Harbor.

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