States right to determine their own laws.
Not a ‘right to do’ something. The right NOT TO BE told what they can or cannot do, outside of the enumerated powers listed in the Constitution.
Plus there was more to the war than “we hate slavery so we are going to war with you”. You see that don’t you?
The South was going to withdraw because the North was telling them what they had to do (yes, regarding slavery).
Preventing the South from withdrawing was the goal, in all actuality, because the North would have been bankrupted (longer story there)
Slavery was going away slowly anyway. General Lee (OF THE SOUTH) even taught his slaves to read and write, even though it was actually against the law.
Remember- the USA did not INVENT slavery. It existed for thousands of years. And still exists in some countries.