You say that like its some magic words or something. The United Kingdom also wanted to preserve the Union! We articulated a right for people to leave a Union which they felt did not represent their interests, and so the Southern states did this, just as the founders had done it "four score and seven years" earlier.
There is no moral authority to "preserve" the Union any more than there is to preserve another form of coerced servitude known as slavery.
If people are free, then they are free to leave the Union if they wish. If they are not free to leave, they are subjects.
But here is the weird twisted logic you employ. "The slave states must be compelled to stay in the union, and to encourage them to do so, we will give them permanent protection for slavery, but when they reject this, we will fight a war to destroy slavery"?
Nonsense. Lies.
It's about money. It never was about slaves.
“ The United Kingdom also wanted to preserve the Union!”
We, the people of the Confederate States, each State acting in its sovereign and independent character, in order to form a PERMANENT federal government, establish justice, insure domestic tranquillity, and secure the blessings of liberty to ourselves and our posterity invoking the favor and guidance of Almighty God do ordain and establish this Constitution for the Confederate States of America.