There's a third prong - the Junkers ( Prussian big landowners with a longstanding , serious military culture ) based leadership class died out. Paul von Hindenburg was one of the last of them.

That led to a major power vacuum, and SFAIK, historians will use a power vacuum in explanations every time.

Ditto Russia. The enfeeblement, isolation and stubborn insistence on doubling down on absolute monarchy of Nicolas II contributed to that disaster.