the csa was never a nation. No real nation ever formally recognized their legitimacy.
That is the view of the northern states as is the belief that Appomattox “proved” the South was wrong.
That is exactly correct in the same way that Andrew Jackson “proved” Cherokees were wrong to want to live east of the Mississippi; Sherman “proved” Indians were wrong to want to live anywhere; Germany “proved” Poland was wrong; and Janet Reno “proved” the children at Waco were wrong.
What Appomattox really proved was that 22 industrial states could beat 11 agrarian states by using modern, total warfare - and clever propaganda.