The big what-if question.
Both Hitler and Roosevelt believed that war was inevitable, and they were both probably right. Restraining the war machine in December of 1941 might have bought some additional time for Germany in the Med and (possibly) in the skies, but would have forced the Kriegsmarine to forego an offensive that it believed could win the war. And in the end, the Americans likely would have joined the conflict anyway, perhaps with less experience, but with greater overall preparation to make a decisive commitment.
What if Germany had never declared war on the United States during World War II?
Scholars and analysts have long wondered whether this represented one of the great “what-ifs” of World War II; could the Germans have kept the United States out of the war, or at least undercut popular support for fighting in the European Theater, by declining to join the Japanese offensive?
Was the decision to declare war on the United States, effectively relieving the Roosevelt administration of the responsibility of mobilizing American sentiment for war in Europe, among Hitler’s greatest blunders?
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Probably not. Washington and Berlin agreed that war was inevitable; the only question was who would fire the first shots.