America seemed quite isolationist at the time. It wouldn't be hard to imagine a world where they never entered into either World War if they weren't given a good cassus belli.
As I am not American, can anyone fill me in on what the high school kids are taught about their entry into WWI and WWII?
Hmm... I've spent a modest amount of time studying WWI and WWII history on my own over the years since school, so it's a little hard for me to disambiguate what I remember from way back then, from things I've learnt more recently. But as best as I can recall, what we were taught in high school was basically:
(main) reason for entering WWI:
• the sinking of the Lusitania
(main) reason for entering WWII:
• the Japanese attack on Pearl Harbor
I don't think I learned about the Zimmerman telegram in high-school, or even college. I think I learned about that later. And I had never heard of the Black Tom Explosion until today.
Germany's move to resume unrestricted submarine warfare was a calculated gambit to try to push Britain, and then France, out of the war before the US could join the European theater. As part of this gambit, they tried to enlist Mexico as an ally to distract the US, hence the Zimmerman telegram--which was such a perfect note to enrage the US public that it was actually widely suspected to be a British intelligence plant.
And we did cover all of this in both 7th and 11th grade US history in my school district.
The reasons for entry into WWII were presented as more complex, having to do with differences of opinion in the US regarding entry and so forth.
For example, although Pearl Harbor was presented as a precipitating event, it wasn't really presented as the thing that led to US entry. The Lend-Lease Act, for example, was presented as a sort of indirect foray or entry path into the war; Pearl Harbor was presented as a last straw or a formal excuse, one that would have been triggered by Germany or Japan in some way or another if it weren't for Pearl Harbor.
I think a lot of the WW1 curriculum was focused on Europe and the events leading up to the war, the diplomatic entanglements, the senseless humanitarian disasters, and the impacts it had on the world with the Lost Generation.
Same, I am really shocked this was never taught in either setting for me(US based). and wonder what is the rationale behind this but suspect its due to alot of things. It shows an attack on US soil at the most important US city, which damages the statue of liberty(a symbol of the US). I would love to know why this is not in every textbook in America when relating to WW1.
"We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part [Boghardt disagrees with this translation, giving a weaker "consent" rather than "understanding"] that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you. You will inform the President of the above most secretly as soon as the outbreak of war with the United States of America is certain, and add the suggestion that he should, on his own initiative, invite Japan to immediate adherence and at the same time mediate between Japan and ourselves. Please call the President's attention to the fact that the ruthless employment of our submarines now offers the prospect of compelling England in a few months to make peace.
I'm only really scratching the surface, but the US just never likes saying we're an imperialist nation who's colonies were being invaded by Japan. It's still the argument used to deny statehood (or independence) for Puerto Rico
Because of the American oil embargo against them (Started on August 1st, 1941. 80% of Japan's oil was imported from the US, and as of December 1941, they had three months worth of supplies left.)
Why was there an oil embargo?
Because FDR wanted them to stop their war in China. (Which started in 1931, by the way.)
Pearl Harbor did not just magically appear out of the blue, with no prior context. In both the precipitating event (Peace talks over aggression in China), and the triggering event (Surprise attack on Pearl Harbour) Japan grossly misjudged FDR's willingness to employ the nuclear option. (Pun intended. And yes, I know that it was Truman who ordered the bomb to be dropped.)
Something like that anyway. It's been a while since I read up on all of this.
The UK actually declared war on Japan nine hours before the U.S. did, partially due to Japanese attacks on Malaya, Singapore, and Hong Kong, and partially due to British Prime Minister Winston Churchill's promise to declare war "within the hour" of a Japanese attack on the United States.
I had forgotten the part about the attacks on Malaya, etc.
I think the powers of the president are the real driver for such intervention. We always have interests on one side more than the other, and they can't resist meddling. FDR flagrantly took sides in WW2 which probably made getting pulled into that war inevitable.
As Japan saw it, the US oil embargo forced Japan to choose between war or a humiliating capitulation to US demands. 
The major takeaway is: never force a near-peer to choose between humiliation and war. Aristocrats are insulated from the true cost of war, and will always prefer it.
But nearly 40 years of right wing assassinations and military intriguing since the crushing of Russia in 1904 had created a monster. The entire country believed they were superior to other Asians, deserved to rule them and any one who refused to help were “humiliating” them.
There were Japanese leaders who realized a war with the US was unwinnable (including Yamamoto), but taking that position publicly was suicide.
There are similarly jingoistic contemporary Asian powers that pretend everything offends them. It's dangerous.
The US defeated Spain in a war of Spain's making, and the US then received those territories as a settlement because Spain lost. The US ended colonial dominance of the Philippines and set them free to become an independent nation beginning in 1934.
And Puerto Rico? They persistently seek to remain attached to the US. No wonder: their GDP per capita is double that of Chile and triple that of Mexico or Argentina for contrast. Amusingly, it's even higher than Spain's GDP per capita.
Similarly the US didn't wake up one day and decide to invade Mexico as an expansionist policy. Mexico started a war with the US and lost, some of their territory was ceded because of their mistake in starting that war. Historically it's a bad idea to start wars with vastly more powerful neighbors, it has commonly ended in losing territory.
Despite being a superpower for seven decades, the US has maintained stable borders with its neighbors. It could have spent the last seven decades taking territory in North America, and it has chosen not to behave that way. For example the US fairly splits the Gulf of Mexico with Mexico, politely following reasonable border lines rather than going by who is more powerful; contrast that with what's going on in the South China Sea.
The Spanish-American War was driven more by the US political intrigue than Spain's. The USS Maine's explosion in Havana harbor (where it had been sent to help protect US interests in the Cuban War of Independence) drove American paranoia about Spanish interference, which led to the US declaring war to deprive Spain of its remaining territories in the Americas.
> The US ended colonial dominance of the Philippines
The US Pacific detachment happened to be near Manila when war broke out, handily destroyed the Spanish fleet there, and then assisted the ongoing Philippine revolt. And then took the Philippines as a colony, suppressing the revolution they had just been supporting not a few months earlier. They only started granting the Philippines its independence in the 1930s.
While American colonization was arguably more benign than other countries, don't kid yourself that it wasn't colonization, and don't kid yourself that it was done in accordance with the wishes of the local populations.
> Similarly the US didn't wake up one day and decide to invade Mexico as an expansionist policy. Mexico started a war with the US
American settlers started squatting in the region of Texas. When Mexico tried to assert its authority over Texas, the region rebelled and formed an independent country, which Mexico objected to but did accept to some degree as a de facto resolution. However, the Republic of Texas tried to claim as much land as it could--ideally as far as the Pacific Ocean, but usually cited as the Rio Grande border. After the US annexed Texas, it took the Rio Grande as the notional border, and moved its troops into the disputed region to provoke Mexico, taking the territory of Alta California as its prize in the ensuing conflict.
Functionally speaking, it's actually not entirely unlike the Russian annexation of the Crimea in modern terms, if the Ukraine were to go to war against Russia's violation of its territory.
I’m sorry? I thought the spark was the explosion of the USS Maine, which was swiftly blamed on the Spanish despite evidence for this being slim and a public itching to help out Spanish colonies in the Caribbean. The United States really did seem to have expansionist policies at the time.
> Mexico started a war with the US
Because American settlers started living in Mexican land?
This is about 3-4 years ago.
EDIT: One other thing of note is that what is taught will vary state by state, as they each set their own curriculum's. I went to high school in Texas.
We are taught that the US remained isolationist after that, being very reluctant to enter WW2 and in the end only joining about 2 years after it "started".
For Commonwealth countries, the war began with Germany's invasion of Poland in 1939. For the Czech Republic, it started in 1938. In parts of Asia, the war began even before that, with Japanese aggression. For some countries in the middle east, WW1 never really ended. But we can all agree that the Americans were pretty late to the party and it's weird when you hear them say that "WW2 began toward the end of 1941 with Pearl harbor", at which point much of Europe was already being crushed by the Nazis.
Some historians argue that the entry of the US into the war and the campaigns the US was involved, often in joint action with the French, in addition to the UK / Commonwealth campaigns of 1918, in served to push the Germans to the point of collapse in 1918 when the general expectation of the allied leadership was that it would take until 1919 to force the Germans out of the territories they occupied.
Then I read about the Canadian Conscription Crisis (WW2) and learned that MacKenzie King was very opposed to going to war and preferred appeasement. His rationale was understandable - it was basically that any war would result in massive upheaval across the world, including Canada, particularly straining English-French relationships (as it did in WW1).
Canada ended up sending a volunteer division early on, comprised almost of entirely of English speakers. The French army ended up being called "Zombies" - trained, but never deployed. The one English division was run ragged - huge amounts of PTSD since they couldn't be relieved (there were no other soldiers to replace them).
Of course, conscription was eventually pursued (after a referendum) and Canada played a very large role in the European theatre. But the first few years were quite the cluster.