I'm surprised such a superstitious reply is so highly-upvoted. There's no "WW3" any more than there is time travel or blue smirfs. It's a hypothetical, but you're talking about it like it's an inevitability. That's just not logically-sound thinking.
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).
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".
throwpoaster|2 days ago
It was only when one stood back to regard the whole picture that it became clear that something larger was happening.
OP is making the same point.
decimalenough|2 days ago
https://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".