Americans as a whole love the tired and worn out myth of loving their freedom, their constitution and their rights and being willing to die for them. Nothing could be further from the truth, well at least in the North.
In the 1850s, as the Republican Party came to power, they and their Whig allies, in order to help their Marxist oligarchs and financial backers, while building the Imperial Federal government, placed heavy export duties on American goods. At that point, most of those goods came out of the South. Thus it came to pass that 30% of the American population was paying for 70% of the Federal budget. The government was growing quickly, making an onerous yoke upon the people. However, the German/English stock of the North seemed to enjoy this, while the Scots Irish of the South chaffed. As such, at this point, with the election of Abraham Lincoln, a dedicated Red, the Southern states, in their individual assemblies voted overwhelmingly to secede, as was their right at the time under the US Constitution.
Lincoln and the Republicans would have none of that. The problem was, much of the North was against any kind of war and while choosing not to leave the Union, actively supported the South's rights. To that end, Lincoln suspended the right of Habeas Corpus and without charges, began the mass arrests of his enemies and critics.