I don't think you have thought that through. For example, what was the reaction of the South to the election of a Republican President? What do you think would have been the reaction of the whites in the South had an amendment abolished slavery? What do you think the reaction of the blacks in the South would have been if an amendment abolished slavery? Do you really think the war, the killing, the destruction, and all the hard feelings could have been skipped? The South was going down either way, son. Don't you realize that Taney's decision in Dred Scott meant War?
Dred Scott, a 7-2 decision, was accepted by the South. You seem to be saying Cain decided to murder the South after Dred Scott.
If that's the case - “the South was going down either way”, as you say - then the North really did decide to overthrow the pro-slavery U.S. constitution by using violence.
It is unusual for a northerner to state as bluntly as you did that it was the North that rebelled against the constitution and the “law of the land.”