Just as it was the free decision of a State to enter the Union, it's the free decision of a State to leave it. Simple as.

>and that as Free and Independent States, they have full Power to levy War, conclude Peace, contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do.
- The Declaration of Independence

>Yes, our country started by declaring independence from the British Empire
>But nooooooooo you can't declare independence from us now!!!!!!
How did the North respond to this? Legally speaking, weren't the southern states within their rights to secede?