When Hitler invaded Poland, it took all of two days for basically all of Europe to realize that they were about to replay the Great War (which we now call WW1).
replyhttps://en.wikipedia.org/wiki/Declarations_of_war_during_Wor...
Of course it took longer for it to blow up into a truly global war (Pearl Harbor etc), but a conflagration across Europe is hardly a "small regional war".
Declaring war is one thing, but if you look at how leaders actually responded it's another (notice the 8 month gap from the declaration of war, into actual fighting). They were still willing to negotiate with Hitler, because most western leadership also wanted the communists to be destroyed and thought Hitler would do just that without attacking them. They were willing to push for this literally until the tanks were invading their streets.
replyOnce Hitler invaded France the "phoney war" turned into a real war. [1]
Hitler attacked several countries before attacking Poland.
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