This was one of the pivotal points of WWII. What would have happened? How would the U.S. justify joining the crusade against Hitler's Fortress Europa? Thoughts?

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Carpe Diem

I think that by the end of '42 we would've been at war with Germany anyway due to the sinking of US merchant ships bound for Britain, unless our total effort was focused on the defeat of Japan, and no more lend-lease goods were sent across the Atlantic.
Admittedly, the war in Europe might have been considerably lengthened, if not 'lost' entirely without US aid.
For example:
Without lend-lease to Russia, she may have sought an armistice with Germany if only to gain time to re-arm for an eventual counterstroke.
Without US aid, Britain would almost certainly have fallen due to the U-boat 'blockade' and raids on her commerce shipping on the open seas.
Now it's Spring 1943, and the Greater German Reich encompases the greatest territorial conquests Germany made during the war, with no powerful foes left in the ETO (The Russians are an uncertainty at best, but now face a properly entrenched and replenished Wermacht)
Presumably, Japan is weakening if not on the ropes due to the US concentrating on them alone.... We have the economy geared up for war, but do we have the will to invade Europe WITHOUT provocation?
Unless a 'Lusitania-like' incident occurs, perhaps not...

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Killjoy

yeah i tend to think the US would have continued lend lease if Hitler didn't declare war...eventually Germany would result in sinking US merchant ships..and the US would pull a thing like in WW1.

I think that we would have gotten to a point though where our merchant ships would have ceased going to England....because it had fallen. Its not doubt we would have fought a war in the Pacific though.

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Out side is America!

I think that the US would have eventually gotten involved in the war just because they can't stand around and watch such a mass murder of people happen. If they had not joined in participation in the war, big time events such as D-day would either not have happened or not have been such a success.