It's obvious that the southern people were not willing to abide by Lee's idea in the first letter that the government could not be sundered except by the whole people.
He abandoned that idea himself and took up arms against the lawful government -- the government the nature of which he correctly characterized in the 1861 letter.
Walt
And it was sundered by the whole people of the southern states. Seconded by the attack of the northern states upon the south.