because U. S. citizens were fighting to preserve the American Experiment, which they felt was important not only to themselves and their posterity but to the people of the world. To them, it truly was a struggle to assure "that government of the people, by the people, for the people, shall not perish from the earth."
The Confederacy Used the U. S. Constitution as a blueprint of theirs. Keeping in place the protections for States Rights and Limiting the Power of the Federal Government. And People in the Confederacy Voted. Many would argue that the Confederate Constitution was the Protector of our Original Constitution.
Lincoln and the Republicans, did not protect the Constitution during the War. They purposely denied Liberty to citizens, arrested their Political opposition, arrested citizens for their Thoughts, and In-Actions. I don't think any of this, is as the founders wanted it. Nor did the Founders Think you should use Force against Citizens to do something, against their Will, like staying in a Union, they didn’t want to be a part of.
Republicans changed the relation of the Federal Government away from the Founders Design. Founders were for Strong State Governments.
Would Revolutionary principles, include Attacking Native American peoples in their sleep. Excluding a race of people from Immigration? Actually anyone but White. In 1870 Republicans reaffirmed White in our Immigration Laws. Nullifying the Civil Rights Act? Human Trafficking? Opium Trafficking that help to enslave a estimated 15 Million Chinese? And eventually bringing Opium to our shires. Don't think the North had a moral Advantage.