The old, rich, and stupid. One of the things that has been blowing my mind recently is the awareness of how many wars happen as a result of accident, miscommunication, and institutional inertia. The Japanese attack on Pearl Harbour started off as a hypothetical 'how could we win a potential war with the US', then over time, gained so much momentum that even though its principal architect thought it was a very bad idea, and although it was obviously not in Japan's national interest, it ended up going ahead.

Wasn't there a whole ordeal with competing entities, even within national organizations and army branches, who were all zealously entrenched in their own little jurisdictions?

That too - but that's present in any state. Japan just had the weirdest combination of resting all authority in the emperor, while having a strong tradition of the emperor never exercising any practical authority. So you get stuff like the creation of a puppet state in Manchuria essentially against the will of the Japanese prime minister.

I think the basic structure of a leader that theoretically has absolute power, but practically speaking is a kind of empty suit, is actually pretty generalizable and common. Japan is an extreme example, but I wouldn't be surprised if the Iraq war was the result of a similar combination of institutional momentum and leadership vacuum[0].