I have never really understood why Hitler jumped all over declaring war on the US after Pearl Harbor. We were certainly leaning against him in the Atlantic but he had no real, overriding reason to add another large, really pissed off, industrial country to deal with and from what I have read, the senior Heer leadership was taken aback by his petulance in declaring war without consulting them as to the Werhmacht's ability to fight the US, the UK and the Soviet Empire all at once. But I guess that in Dec 1941, he was still expecting a Soviet collapse and he thought the Brits were also on their last legs and tied up trying to hold on to their overseas holdings, such as India. I also wonder if there was a bit of contempt for the ability of the US to make the substantial contribution as quickly as it did.

Japan didn't seem to want to reciprocate, they didn't attack the Soviets after 22 June 1941, but I guess that was in large part due to the butt-whupping they had received a few years earlier and they were looking at a critical oil shortage that could not be rectified by taking oil-less Siberian land.

I feel confident that the US would have eventually joined the European war even without a Dec 1941 German declaration of war, I just can't speculate how many more incidents like the Reuben James it would have taken.

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Best Regards,
JW