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I had earlier posted this question somewhere on the Historynet website about why the Japanese decided to attack the United States; but at the time didn’t realize you existed, Mr. History. None of the usual explanations have fully answered this question, so I ask you now:
Why did the Japanese leadership think the US would step in if Japan used the opportunity of a full-blown, life-or-death war in Europe to pick off the now vulnerable European colonies in Asia? The US being a vocal critic of the institution of empire would never have committed troops to protect Europe’s eastern colonies.
America’s major military holding–the Philippines–didn’t have the oil, rubber or raw materials the Japanese were primarily looking for. With the isolationist US left in peace, Japan’s war would tidily have been completed in a few months and (though they couldn’t have known it at the time) with little chance the later war-devastated former colonial powers ever returning to take them back.
This miscalculation by Japan’s military rulers has to rank amongst the most cataclysmic in all military history. And yet, nobody that I’m aware of has ever even posed the question.

What gives, Mr History?

Keith Gentile




Dear Mr. Gentile:

The reason nobody has asked why the Japanese went to war against the United States is that it had ample reasons for it by the fall of 1941, albeit much of their own making. The United States had generally enjoyed relatively friendly relations with China, but took an ambivalent stance, even after the Marco Polo Bridge Incident on July 7, 1937, gave Japan an excuse to launch a full-scale invasion. Even while fending off isolationists, in 1940 and 1941 President Franklin D. Roosevelt began supplying increased arms under Lend-Lease to China, even while the United States shipped oil, iron, steel and other commodities to Japan. In January 1940, however, Japan abrogated its existing treaty of commerce with the United States. In August 1940 Japan declared its intention of creating a Greater East Asia Co-Prosperity Sphere, with the European powers ousted and (in practice) Japan exploiting the continent and its resources all by itself. On September 27, 1940, Japan signed the Tripartite Pact, committing itself to alliance with Adolf Hitler’s Germany and Benito Mussolini’s Italy—countries that Roosevelt already eyed with hostility. In mid-1941 Japan signed a neutrality pact with the Soviet Union, designed to free up its concerns about the Mongolian-Manchurian border and allow further military activity in Southeast Asia. Things came to a head on July 21, 1941, when Japanese forces entered nominally neutral Vichy French-held southern Indochina. On the 24th Roosevelt requested that the Japanese remove their forces from there and when the Japanese failed to respond, on the 26th the United States and Great Britain placed a full embargo on oil and other strategic materials being shipped to Japan. The Netherlands government-in-exile followed suit with an embargo on such materials from the Netherland East Indies on the 26th.

At that point the Japanese militarists had painted themselves into a corner. They could withdraw their troops from China and Indochina, but they could not countenance the loss of face and material loss of existing conquests that would entail. They therefore stepped up a strategy to obtain the resources necessary to pursue their war against China by force, through a war against the British Commonwealth and the Netherlands. That would also require eliminating American naval power and the seizure of its strategic bases in the Pacific.



Jon Guttman

Research Director

World History

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