There is little doubt that the US embargoes on Japan pushed an already aggressive Japan towards Pearl Harbor. Japanese Navy doctrine had already been contemplating a conflict with the US and this gave them the choice of backing down or going to war.

Beginning in 1938, the U.S. adopted a succession of increasingly restrictive trade restrictions with Japan. This included terminating its 1911 commercial treaty with Japan in 1939, further tightened by the Export Control Act of 1940. These efforts failed to deter Japan from continuing its war in China, or from signing the Tripartite Pact in 1940 with Nazi Germany and Fascist Italy, officially forming the Axis Powers.

To a large extent, US pressure seems to have been in response to Japanese aggression in China. Aggression that involved atrocities such as the Rape of Nanjing.

What was the reason for the strong support of the US vis a vis China? After all, most Western countries didn't usually intervene all that much to protect poorer countries. All the odder since the US had strong isolationist tendencies after WW1.

  • Was it due to colonial ambitions of its own? That's possible, but the US could have just stated its own red lines with regards to Guam, the Philippines, Hawaii and sundry, without embargo.

  • Was it part of the generalized aggravation the West seemed to have with Japan's behavior in China, which many saw as putting the death knell to the League of Nations?

  • Was it sympathy by the US public from observing Japan's actions in China, including the Panay Incident and reporters covering Nanjing? i.e. a national sense of altruism and concern for the well-being of another country?

  • Did FDR want to put in the groundwork for blocking the Axis, before the US had officially taken a position? Even then, the earlier embargoes were before Japan joined the Axis.

(That the US may have misread the possibility that the Japanese would undertake a suicidal war isn't really part of this question unless it was considered such a remote likelihood that it would not factor in US planning. Even then, these embargoes affected US exporters, who presumably lobbied the government not to put them in place)

P.S: Please understand that this is not a "poor Japan was forced into the war by the USA" question. Japan reaped what it sowed. Nor am I asking about the potential strategic challenge by Japan. Only why the uncharacteristic "vigor" of US diplomacy at a time of isolationism? Was it public-led? FDR-led?

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    Also, Japan & the USA (among others) signed treaties, specifically the 9 power treaty and Shandong treaties to limit further Japanese expansion into China and maintain the status-quo open door policies and then Japan violated these agreements. Violating treaties doesnt usually go over well with the American govt or public.
    – ed.hank
    Aug 26, 2021 at 12:43
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    @ed.hank totally! what got the isolationist US public to say "oil embargo? no problemo!" by 1940? Aug 27, 2021 at 8:27
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    The degree to which the US was 'isolationist' outside of Europe tends to be overstated. "Guam, the Philippines, Hawaii and sundry" wouldn't be US possessions if it wasn't fairly expansionist in the Pacific.
    – timeskull
    Aug 27, 2021 at 14:09
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    @ed.hank well, not unless America is the one violating the treaties
    – llama
    Aug 27, 2021 at 15:43
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    @llama - yup very true, i was going to add that as a caveat but decided against as it wasnt super relevant to the answer.
    – ed.hank
    Aug 27, 2021 at 16:05

4 Answers 4


Japan was a threat to the US's Pacific territories, and those of other European powers. China was not.

Unlike China, and every other Asian nation at the time, Japan had defeated and humiliated a European power in the Russo-Japanese War. They defeated Russia not only on land, but also at sea where European powers typically dominate. Even if it was the ailing Russian empire, Europe considered the Japanese military a real threat.

Due to its modern and victorious navy and air force, Japan had the ability to project their power across the Pacific. They could threaten US Pacific possessions. In particular, the Philippines.

And Japan was increasingly militaristic and expansionist, whereas China had rarely ventured outside its borders in recent years.

Japanese militarism

Japan was very aggressive and tended to ignore and break international treaties. In 1895 Japan took Korea from China. This lead to the aforementioned clash with Russia in 1905 over their ambitions towards Korea and Manchuria. The European powers attempted to stave off a naval arms race and bind Japan with a series of naval treaties in the 20s and 30s which many in Japan found humiliating and eventually renounced.

The early Shōwa period saw Japan slide from a young democracy into an ultra-nationalist military dictatorship. This lead to concepts such as the Tōa Shin Chitsujo (New Order in East Asia) and later Dai Tōa Kyōeiken (Greater East Asia Co-Prosperity Sphere), the idea that Japan should rule over Southeast Asia; a direct threat to European powers' own imperialism.

To that end, Japan invaded Manchuria in 1931 on a pretense, ignoring international condemnation and withdrawing from the League of Nations. The conflict with China simmered for years until a full blown invasion in 1937.

World opinion turns against Japan

Japan relied heavily on trade with the US and Europe for oil, automotive equipment, steel, scrap iron, copper, and other resources. This in turned fueled their expansion. This profitable trade was left mostly unchecked, the US wishing to remain neutral. But the after the Japanese invasion of China in 1937 news of Japanese war crimes in China and an attack on a US Navy gunboat began to turn public opinion in the US against Japan.

Japan cozied up with Germany and Italy signing the Anti-Comintern Pact in 1936 and later the Tripartite Pact in 1940 identifying the US as their common enemy.

It was increasingly seen as hypocritical and self-defeating for the US to be fueling the Axis war machine.

In April 1939, Maxwell S. Stewart, economist and national chairman of the American Friends of the Chinese People, said before the US House Committee on Foreign Affairs about the Neutrality Act...

Our existing Neutrality Act was enacted with a view to protecting the United States against war. With that purpose I have profoundest sympathy, but I feel that in its present form it stands as a definite menace not only to world peace but to our own national security...

The time has now arrived when an immediate change must be made in the [Neutrality Act] if the United States is not to throw its influence permanently on the side of aggression. For, make no mistake about it, Hitler and Mussolini and the Japanese military leaders are counting heavily on the retention of the act in its present form. They know that as long as American resources are denied to their victims, while they, in turn, can obtain unlimited supplies of raw materials legally they need have no fear of continuing their policy of aggression.

Although this country has refrained from actually inpenalizing [sp] China by invoking the act, the weight of its influence has nevertheless been on the side of Japan. For although our sympathies as a people have unquestionably been on the side of China, we have contributed the economic resources without which Japan could not have carried out its illegal invasion of the Chinese Republic...

In all of this we are not only arming Japan against China, but we are actually arming her against ourselves. If Japan carries its aggressive program in the South Pacific farther and occupies American possessions, it can do so only on the strength of the sinews of war supplied by the United States.

Success for Japan in its illegal invasion of China would also endanger the security of the United States by encouraging potential aggressors the world over. Peace depends upon the general recognition of some standards of international law and equity. Each new victory for the aggressors undermines that protection and threatens to throw the world into complete anarchy.

From American Neutrality Policy page 263.

In 1940 the US passed the Export Control Act to limit sending war material to Japan, a likely enemy, and to also avoid shortages of those same materials in the US when war in Europe and the Pacific seemed increasingly likely.

But oil was excluded. The US and Japan knew an oil embargo could provoke a conflict and both were not ready yet.

Oil for the Japanese war machine

Japan needed oil for their industry and war machine. The US was a major exporter of oil at the time. If the US and Japan came to blows the obvious place for Japan to get oil was the Dutch East Indies (now Indonesia). A simple look at the map shows the concern for the US: the Philippines lies directly between Japan and their oil.

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The US would be in a position to interfere with Japanese ambitions towards the Dutch East Indies. To secure their oil, Japan would have to neutralize the Philippines.

The last straw, seizure of French Indochina

After France fell in 1940, Japan got Vichy France to allow them to station troops in French Indochina which turned into an occupation of Northern French Indochina. In July 1941 the pretense was dropped and Japan occupied the whole of French Indochina positioning themselves to attack Malaya, Singapore, and the Dutch East Indies.

This was the last straw. As many in Japan expected, in response the US, Britain, and the Dutch cut off their oil trade with Japan. The Western Allies felt that Japan could not continue their wars without oil trade, and that the Allies could defend their territories. The Allies were right about the first part.

In December 1941, simultaneous with the invasion of Pearl Harbor, Japan invaded the Philippines. With the bulk of the US Pacific fleet sunk, the cavalry would not come to save them as had been planned. With the US fleet out of action, US forces in the Philippines on the defensive, and the British fighting for their lives in Europe, the Japanese were free to invade the Dutch East Indies 10 days later and begin seizing oil production.

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    This does not tell me why the US went out of its way to confront it early on. Among other things, if the US had still be trading oil with Japan the whole situation wrt Java would have changed: Japan may not have felt the need to attack Java and it would have had less reason to attack the US if it did (something that was, I believe an active point of debate in the Japanese high command). So I see this answer as a bit circular: "once the US confronted Japan, Japan was a threat to the US". OK but why didn't the US wait things out? US sentiment was quite isolationist at the time after all. Aug 26, 2021 at 21:49
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    @ItalianPhilosophers4Monica You're right there is more to it than just "Japan threatened the Philippines". I can flesh it out some more. The US supplied the Japan. The Japanese showed no sign of stopping their expansion. Japanese war crimes in China and attacks on Westerners turned public opinion in the US against them. The US did not want to supply Axis aggression, so they stopped. They, rightly as it eventually turned out, realized Japan could not sustain their military without Western trade.
    – Schwern
    Aug 26, 2021 at 22:03
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    Txs. I'd be interested to know if the general public sentiment demanded FDR push back, early on, say 37-38. Or, opposite, if FDR was getting some resistance in the form of "let's not get dragged into other folks' wars". Racism, by itself, doesn't explain all that much - yes for anti-Japan, but why pro-China then? I mean, it was the right thing to do, but it just seems out of character at the time. Aug 26, 2021 at 22:06
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    @ItalianPhilosophers4Monica I'd say the relationship towards China was "paternalistic". I added a quote from a US House hearing that I feel sums up the whole US viewpoint. A mix of self-defense, paternalism, and a sense of moral outrage.
    – Schwern
    Aug 26, 2021 at 22:48
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    "whereas China had rarely ventured outside its borders." in recent years. China was the largest empire in Asia because it had a long history of expanding its borders.
    – Readin
    Aug 29, 2021 at 3:14

One angle I think a lot of people miss (particularly non US people) is that, being a former colony that had to fight for independence itself, the USA during that period very much liked to identify itself as being an anti-colonial power. Yes, I know that this attitude didn't mesh too well with the reality of its existing position in the Philippines, but this was the way Americans of the era had been raised to feel about themselves. The former Spanish possessions were still fairly new acquisitions at the time, and were justified as pre-existing colonies now being prepared for independence by the US1.

For this reason, there was a lot of natural sympathy in the country for China's position. Like the USA, it was a continental-sized nation, but being taken advantage of by colonial powers. It was pretty clear that given a fair shot, they should be doing much better for themselves and their people than the colonial powers were allowing.

It of course didn't hurt that doing something about this would incidentally help open up a potentially vast market to US trade. This is why the USA made something of a special project of China, going so far as to promote her as a full-fledged member for the UN (at first the allies fighting WWII, but eventually the post-war organization as well).

Japan meanwhile was energetically trying to gather itself its own colonies. Exactly the kind of behavior the US felt there should be less of in the world, not more. The US wasn't really particularly anti-Japan, but they were very much against Japan's militarily expanding colonialism. Japan for their part was dead set on their colonial program, which led them to view any pushback whatsoever from the US as being fundamentally hostile to Japan.

1 - In fact, the Philippines were granted their independence less than a year after the war ended. Whether the war sped up or slowed down that day coming would be a good question.


You answered your question yourself:

To a large extent, US pressure seems to have in response to Japanese aggression in China. An aggression which involved atrocities such as the Rape of Nanjing.

This was an atrocity beyond anything people had experienced, apart from trench warfare. That fact alone was more than enough reason. Most western nation sanctioned Japan, not just the USA.

Another less altruistic reason is the expansion of Japanese influence in China. That wasn't exactly in the interest of America. Compare it with 'Let Germany (prior WO 1 & 2) rule Central Europe. It doesn't affect Great Britain'.

Japan controlling most of China would be the same for the USA as Germany controlling continental Europe for the Kingdom of Great Britain and Northern Ireland.

  • *cough* ... for Great Britain, if ye dinnae mind, laddie. Aug 29, 2021 at 0:45
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    @BlokeDownThePub Okay, as soon as the rest of the world stops calling The Netherlands Holland. :-)
    – Jos
    Aug 29, 2021 at 1:17

One of the catalysts was the "accidental" sinking of the U.S.S. Panay in December, 1937.

This was an American-owned and flagged gunboat patrolling the Yangtze River. The Japanese didn't realize this (or so they claimed) because it was of Chinese make, and Japan was at war with China. The incident was contained but not forgotten when the Japanese apologized and paid an indemnity.

Besides the loss of 43 American casualties, the incident had huge symbolic importance. The Panay had been rescuing American survivors of the Japanese Rape of Nanking, an atrocity that was brought home to the American public by the Panay incident (there were several journalists aboard ship). Naturally, this public sided with the victims and against the aggressors.

A (presumably) accidental sinking of the U.S.S. Maine in Cuba had brought about the Spanish-American War less than 40 years earlier; Americans tended to react strongly to sunk ships, accidentally or otherwise.

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