There were rules agreed to at the creation to the Union. Who violated them? Do serious men take their rules seriously? Does might make right? Because you believe your cause is more just? Would Obama be right to invade “non-gay” states that resist gay marriage? According to Union logic, yes, because leftist “morality” supersedes everything else.
What rules exactly did the North “violate”? Lincoln wasn’t even sworn in yet when the southern states started to succeed. They made it clear that they would if he won even before the election.
As for the much vaunted southern love of states rights, ever heard of Dred Scott? They had no concern for the rights of free states not to have to participate in a system of slavery they considered immoral when they made them treat escaped slaves as property to be returned. And in doing so they made ending slavery a moral issue for the north.