[0.E.O]

He probably thinks the dictionary is some haughty Yankee trick.

Or perhaps the definition of 'unilateral' in the English-Confederate/Confederate-English dictionary is different?

[central_va]

UNILATERAL. 1. a: done or undertaken by one person or party

There were 11 states in the Confederacy, therefore it was not unilateral.

So yes, South Carolina's secession was unilateral, after which it became a plurality of states.

Definition of PLURALITY
1 : the state of being plural
  : the state of being numerous
  : a large number or quantity
2: pluralism 1; also : a benefice held by pluralism
3 : a number greater than another
  : an excess of votes over those cast for an opposing  candidate