Every step backward along the chain of causality is an equally valid reason.
Someone believing the propaganda is as much a reason as someone writing it, or someone ordering that it be written, or someone inventing the casus belli behind it.
It is a fallacy to assert a true root cause in anything, because no event is so cleanly disconnected from the rest of history that you can definitively say that a deciding event is truly independent of all those that came before.
The root cause for any war is psychopath rulers wanting more power and more wealth for themselves. The rest follows from that. Of course, the rulers will be spewing bullshit propaganda to get their peons to go die for them.
The commenter I originally responded to seemed to suggest that there would be a "good" reason for people to go die or kill people in a war.
But enriching his rulers is not exactly a good reason for an ordinary person to kill or die trying. What's in it for him? Wouldn't he much rather not do it?
Someone believing the propaganda is as much a reason as someone writing it, or someone ordering that it be written, or someone inventing the casus belli behind it.
It is a fallacy to assert a true root cause in anything, because no event is so cleanly disconnected from the rest of history that you can definitively say that a deciding event is truly independent of all those that came before.