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Why Did the US Respond in WWII?

By Mr. History
3/21/2017 • Ask Mr. History

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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9 Responses to Why Did the US Respond in WWII?

  1. caracoid says:

    Thanks so much for your reply, and I’m with you all the way up to the last sentence. Why did Japan think the US would step in to protect the European colonial powers’ holdings in Southeast Asia?

    Even if Roosevelt wanted to go to war (and he wasn’t particularly keen on it until the US was projected to be minimally prepared by summer of 1942), it’s doubtful the generally pacifist US public would support declaring war on Japan to buttress the old European empires. Roosevelt would surely have been handily launched bumping down the steps of Congress into retirement.

    Japan could have just taken what it needed from the European colonies without going to war with America.

    –Keith Gentile

    • MC2 says:

      At least arguably though, Japan sealed its fate by signing the Tripartite Pact in 1940. Even if none of the other reasons proved adequate, this alliance alone provided a casus belli for Roosevelt’s domestic sponsors –both political and financial.

      The actual “proximate causes” such as Pearl Harbor merely rendered the venture acceptable to the general public as well. Mind you, none of this excuses Japan’s conduct in any way; but it does help to explain America’s.

      • caracoid says:

        But why did Japan attack the US when they could have avoided a war with the only major country on earth that wasn’t currently fully engaged and tied down in a war elsewhere and just invade those countries’ colonies who have all the resources you need and who conveniently happen to be fully tied down fighting Nazi Germany?

      • MC2 says:

        Surely the oil embargo was a principal reason. Japan was being choked, and had (and has) few natural resources of its own. The opportunity to cripple the US Pacific Fleet–the only real impediment to Japan’s imperial goals) in one stroke was too great a temptation.

        And while it’s obvious to us that it was suicidal on the part of Japan, consider that it took years for them to lose, and even then they didn’t surrender until after two atomic bombs had been delivered.

        Part of the explanation for Japan’s megalomania involves its ‘super-race’ ideology which was every bit the equal of the Nazis’ but which is very seldom held up to the light of modern scholarship, much less mass-media representations.

      • caracoid says:

        Interesting. Especially the last part about attacker/attacked.

        I realize that Japan was under embargo (and it wasn’t just us, Britain and free-Holland both joined in), but why did Japan have to attack the US? Why not just Britain’s and Holland’s possessions, gotten all they needed, but left us alone?

        In that case, would we have retaliated if Pearl Harbor was never attacked and the Philippines, Guam and Wake had been left alone? Would the US have broken with its pacifist stance and gone to war to protect Europe’s Asian colonies? It seems to me ludicrous.

      • MC2 says:

        FWIW, in my view the Japanese were never going to leave the Philippines alone. Not only for the islands’ strategic value but for the moral advantage in liberation: the Philippines were undeniable evidence (for all to see) of the USA’s imperialism far away from its own homeland. We had no business there in the first place: just another relic from the Spanish-American war.

        Meanwhile, about the “pacifist stance”–not so much after several years of full-tilt MSM propaganda, mainly news and magazine article and of course Hollywood movies. I think pacifism peaked around 1936-37 in the USA. Various forces conspired against it, which is sort of outside the scope of the present discussion.

        A couple telling details, though: in 1937 the FDR administration declared that the First Amendment’s free-speech protections didn’t cover radio broadcasts. By 1939, the Code Committee of the National Association of Broadcasters required that all radio spokesmen had to have their speeches reviewed in advance in transcript form. Imagine that flying today! Keep in mind that during the 1930s radio was the only method of getting ‘real-time’ info into America’s homes.

      • caracoid says:

        Hard to see the Japanese giving a damn to make the point the US was an imperial power. Why would invading demonstrate anything? Particularly if their ultimate agenda was the worst kind of imperialism, which it was. They weren’t about to risk the existence of their entire nation by taking on a Goliath to call attention to the global imperialism they themselves were already deeply engaged in and about to accelerate to a new world-beating level.

        BTW: The US as an “imperial power” was always way overblown. Kind of like saying America was just as bad as Germany because the US put Japanese-Americans in “concentration camps.”

        Shortly after taking the Philippines, the Philippinos were rapidly given self rule for just about everything except foreign affairs and US military bases by 1916. Stringent laws were put in place keeping Americans from exploiting the Philippinos, their land and resources. By 1916 a date was set for complete self-autonomy by 1946 (a promise kept, by the way).

        Keep in mind every scrap of land in the Pacific at the time was held by a European colonial power. If the US had pulled out of the Philippines after the Spanish left, a whole slew of imperial powers would have fought to take over: the English, Dutch, French, or Germans. And none of them had any degree of the enlightened thinking the US did at the time. And America knew it.

        You should read how the French and Dutch treated their colonial subjects. The English were a bit better, but at the time they had no intention whatsoever of ever giving away their colonies. Even as late as WWII, they were willing to bleed India dry to finance the war, certainly abetting the famines that took place in India during that time.`

      • MC2 says:

        Found a similar discussion on a blog that I sometimes follow :

      • caracoid says:

        Thanks a lot. I’ll take a look.

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