A great question. I'll Let John C Calhoun respond first:
"The Government of the absolute majority instead of the Government of the people is but the Government of the strongest interests; and when not efficiently checked, it is the most tyrannical and oppressive that can be devised."
"A power has risen up in the government greater than the people themselves, consisting of many and various and powerful interests, combined into one mass, and held together by the cohesive power of the vast surplus in the banks."
Power always looks first to entrenchment. The Federal branch, weakened by design, in the Constitution had been consolidating power very specifically on behest of Northern industrialists and bankers for years. These elites correctly surmised that the South's continued usage of free labor represented a challenge to their drive for control of the western territories as well as trade profits with Europe.
I'm not denying that slavery, an abomination in thought and practice
, was a contributor to the war. It certainly was, but like all wars the elites need people, usually uneducated people, to fight them. These people cannot be brought to sacrifice their lives on the noble cause of "enriching rich men". They need a 'moral' reason. This is where religion and patriotism excel and the issue of slavery went to the front burner.
The problem with American history as it's currently taught is that it leaves large gaps in knowledge for important events like the Civil War. Usually that knowledge is economicly based. The reason for that is clearly to keep the majority of people unaware of the mechanisms of a system designed against their interests.