Lincoln wanted to try many southern leaders on charges of treason for seceding from the Union but NOT ONE PERSON WAS EVER TRIED and all charges were eventually dropped! Why not? Because almost every constitutional scholar of the time advised him that the prosecution WOULD LOSE. It would no doubt have been appealed to the Supreme Court and there the Union would have lost, too. What would that mean? Basically what we Southerners have always held, Lincoln conducted a war of agression and conquest.
BTW, the definition of a "civil war" is a war fought for control of a country. The Confederacy wanted only to control itself and the Union could do whatever it wanted.
Our first act as a nation was to REBEL against the authority of the Crown, not secede. Please get your terms straight.
And the Union considered the Confederacy to be engaged in an insurrection. According to the Union, it was a civil war. The winner names the battles, and the winner names the war.