So your telling me that the American public would have been fine with attacking another country in Asia for invading a place that they have never heard of as part of the same European war that you said they wanted to stay out of. In think your conflating the opinions and desires for conflict of the Japanese from the American government meant that the American public would have supported the war. Seriously? How do you sell that to depression America?
Yes, because thats essentially what would've happened. In fact I'll give you a basic historical background because I'm not familiar with the historic background that lays out the reasons of why the US would get involved in the Pacific as opposed to Europe. The reason it's is I prefer to study Europe in WW2 as opposed to the pacific, but more importantly it goes into American Imperialism which I am even less familiar with.
Now we have to go back to then Washington was President and the French Revolution happened. When France asked for help Washington basically did nothing because it wasn't in our interest as a new nation. This was the begining of the traditional view of "It's Europe's problem." It all stems from that. This is why America was never really involved in any European affair in Europe be it Napoleon, the Crimean War, all those socialist revolutions, and even WW1 untill the Zimmerman Telegram.
Now lets fast forward to post US Civil War. America was industrializing and getting her own Empire to spread civilization to the uncivilized in addittion to a interest in a navy which requires naval bases. Where can America get these naval bases? Africa? It's crawling with various European states that all have claims all over the coast. No go, unless you want to fight over it. But then there is the pacific and all of her unclaimed Islands.
America would claim some of these in order to make them naval bases, especially after the Spanish-American War with the acquisition of the Phillipines. America also had great economic interest there. As one person realized that America needed a market for all their goods and this person said "Geography answers the question! China is our natural customer!" Now in addition to economic interests and her security interests in protecting her far flung possessions being Hawaii, Guam, the Philippines, etc, notice how none of them are threatened by anything coming from Continental Europe. There aren't Corsica or Sardinia which can be easily threatened by mainland France or Italy.
So which nation that is industrialized has a close home base to threaten these interests? The obvious answer is Japan. Even the Washington Naval treaty tried to minimize the threat japan posed by limited the number of battleships Japan could have relative to the rest of the great powers. The argument being that the colonial powers had to split their navies to defend their far flung possessions, the US had to split her navy between two oceans, whereas Japan could concentrate her Battlefleet.
Now lets look at this even further with the situation in Indochina with started the oil Embargo and the Southern Operation. Now if Japan had French Indochina, and the East Indies, the Phillipines are put in an impossible position, more so the whatever position they may be in before. Where as before the Phillipines had to worry about a theoretical Japanese Attack from Roughly NE, now it cinludes the W, SE and S. that three additional directions to stretch even few resources. This threatens the balance of power that all of the great powers tried to preserve through the treaty, but which the treaty completely failed to do because of Japanese imperial ambitions.
Now even if you don't think the US would get involved what you think doesn't matter because the Japanese DID believe America would get involved. Because the Phillipines served as a natural spot to sever any raw materials from the East Indies with not just naval bases, but also bombers. The US had already embargoed Japan for taking Indochina in addittion to aggression in Indochina. Japan also had other raw materials embargoed from the East Indies and saw these as acts of aggression. It wasn't hard to imagine that if Japan moved without taking out the Phillipines that the US would get involved militarily.
Infact the US even made plans with the UK and the Netherlands to help protect each other in the event Japan attacked any of their territories. These talks however where in secret. However FDR did war that the US would react if she attacked of her "neighboring countries" (those she wasn't already at war with) in 1941.
However I would very much like someone who is more familiar with what I have said then I to give you a better explanation.
