Williams is correct. The hostilities did not begin until the hot heads in Charleston fired on Fort Sumter. The States voluntarily formed a union. A State can voluntarily withdraw from said union. Whether the remaining States allow this to happen or not is another matter. Power is not always right, but power is always power. Kinda like the vehicle and pederestrain. The pederestrain has the right of way over the vehicle. The trouble begins when the pederestrain exercises that riight.
A state can secede, by constitutional amendment, perhaps by mere federal law, or by successful supreme court case.
No state can by itself secede. The Union wrote the declaration of independence, the union was made perpetual by the articles of confederation, and the union was made more perfect by the current constitution, to include its provisions for amendment.
The precedent denying secession by state action alone is Texas v. White.