[slumber1]

But even when the new Constitution made secession illegal, the impulse to break up stayed strong.

The constitution made secession illegal? Which article contains that clause?

[Alter Kaker]

The constitution made secession illegal? Which article contains that clause?

The Constitution only provides for the addition of states to the Union. It does not provide for secession. The Supreme Court ruled, in Texas v. White, 74 U.S. 700 (1869) that the Constitution is therefore a contract - binding on all parties unless ALL parties agree to dissolve it - and just as one party cannot unilateral tear up a contract one state cannot unilaterally secede from the union.