Why would you assume that my answer would be "one man"? It was an incredibly complex conflict that was really a collection of smaller regional conflicts with various allies between them.
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There's no singular cause of WW2.
Because basically all of those reasons are the same as WWI but amplified by the restrictions (manufactured economic crisis) posed upon Germany at the end of WWI.
That is why I said it can be viewed as the same war.
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(Imho - anyways it's literally just semantics, perhaps propaganda of the victors a bit.)
Much like (the recent-ish) Russia in Ukraine - it's usually not viewed as two separate wars, one in 2014 & the other in 2022. Bcs it's the same thing, it was oblivious that it isn't over & both Russia & NATO/Ukraine have all been actively preparing each year.
However, in retrospect, many people would say when Germany invaded Poland. That said, USSR and Finland were already fighting at that point, as well as Japan and China.
Yeah, Japan in China started basically in 31 (13 years after official end of WWI, a much more European thing), whereas Germany's first foreign move was the military invasion of Austria in 38.
White cat (codename Fluffy_Lamp) is the bait while the black cats (codenames Velvet_Ninja_Assassin & Fuzzy_Moth_Liquidator) are the unseen executioners.
Months after assassination of Ferdinand the actual fighting began, and most projected it would be just anther war (common at the time in Europe, tho less common each century). People living through it knew nothing about it upfront.
We wildly think of WWII beginning with the invasion of Poland, but it took months for everyone (England included) to realise it wasn't a war between two countries.
Not to mention how WWI & WWII are basically the same war in two seemingly inevitable parts.
And we have had a ton of proxy and/or cold wars between Russia & USA since WWII ended.
Or just preemptively reply with the second bit.