A large portion of the American colonists were loyal to the crown in 1776, but the states still successfully seceded from Great Britain. It is fair to say that the loyalists and the patriots were considerably intermixed within the colonies.
Not all Southerners wanted to secede from the union in 1861, but most supported the South when it was invaded.
All a state needs today, in order to legally secede, is a voting majority who wants it. Those who don't can leave the state or live with the decision. This is not to say that the federal government would allow it without a fight, but once again their opposition would be in opposition to both constitutional and natural law.
Buchanan also claims that the issue of secession was settled at Appomattox. On this point, Buchanan is dead wrong. The idea that a constitutional question can be settled by force is to deny the rule of law and the long-held principle of "the consent of the governed." As Jefferson Davis wrote while in prison at Fort Monroe: “A question settled by violence or in disregard of law, must remain unsettled forever.” He was speaking of the right to secede. He was partially correct, but not on whether the issue "must remain unsettled forever." As he himself stated previously, “The principle for which we contend [i.e. secession] is bound to reassert itself, though it may be at another time and in another form.”
The principle is reasserting itself, just as Davis predicted.
Read Buchanan's essay here.
See Related Post from American Renaissance here: Secession: It's Constitutional