re: Nothing new
I'll readily agree with your conclusion here that it's nothing new for leaders to mask the real reasons for war with an emotional overlay that appears to provide legitimacy.
The issue of slavery, I would submit, was used to galvanize the South into rebellion, but the war was actually fought over the issue of the Tariffs of Abomination, which the agricultural South hated but which the industrial North was reluctant to give up.
Fort Sumpter, I recall, was a tariff collection point.
S