A few thoughts/questions:
Isn't the question over the cause of the war different than question of involved individuals' motivations? While of course it's true there were diverse and varying and unconscious/secret motivations, that's *always* the case, and doesn't mean it's impossible to determine historical causes.
In the focus on motivations, you write about and speculate about motivations for adopting one or another narrative. Are the competing narratives only to be measured by these purported motivations? What place does historical evidence have?