[Salamander]

“We the people of the United States, in order to form a more perfect union”

And what is a union?

A voluntary contract or agreement.

Anything less is a conquest, by force.

Oh, wait.

Never mind.

[CodeToad]

Even the federalist #10 states the States have a right to dissolve the union. Lincoln dissolved the union and conquer Ed the States.

[BroJoeK]

Salamander: "And what is a union?
A voluntary contract or agreement.
Anything less is a conquest, by force."

The US was founded on mutual consent and our Founders considered that only mutual consent or necessity should break us apart.

Neither mutual consent nor necessity existed in 1860.
So Confederates seceded "at pleasure" and soon declared war on the United States, both actions illegitimate in our Founders' eyes.