It was about states' rights to perpetuate the system of slavery. Had the confederates taken a stand for the defense of states' rights on some other issue besides slavery, they may have had a defensible point. That they wished to exercise their "rights" to keep a class of people in bondage was a violation of the laws of nature, and of the intent of the founding charter of the nation.
More accurately, the war was about a group of states that didn't like the outcome of a constitutionally valid election, and they wanted to take their ball and go home. Petty, childish, and in the end, tragic.
Awful lot of people died for something they didn't own.
Show me a historical factual quote of a Southern diplomat stating that the only reason their state was voting for succession was because of slavery....please...
If the results weren't so tragic for so many people on both sides of the conflict, the arrogant, ignorant pretensions of the Confederate secessionists would be worth a lot of laughs. What a pitiful and inept gang and like you say, history provides few examples of such shortsighted petulant childishness.