Why is it hard to put an exact due date on the start of world war 2?

Because it was very gradual

Explanation:

Although WWII really started when Germany invaded Poland and went behind Russia's back, it was a very gradual rise of tension in Europe that eventually broke out into WWII.

operation overlord was the codename for the battle of normandy, the allied operation that launched the successful invasion of german-occupied western europe during world war ii. the operation was launched on 6 june 1944 with the normandy landings

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