Just my two cents:
Waging war on the states is a "treasonable" offense. Incidentally, suspending habeus corpus only when states are "in rebellion" is allowed according to the US Constitution.
Some advocates of Lincoln state that he did NOT commit treason because the states had seceded---they acknowledge that they did, in fact, secede. If that is the case, then the ratification of the 14th Amendment falls into question.
Other advocates of Lincoln argue that the states did NOT secede, although they 'tried'---if this is the case, then yes, Lincoln DID commit treason by waging war on them. Seceding is NOT rebelling. Rebellion is insurrection, or uprising. Revolting, violent revolution---these things are acts of rebellion. But saying 'ok...I'm out'---that is not rebellion. That is leaving peacefully.
So yes. According to advocates of Lincoln that say he "suppressed the rebellion" are historically inaccurate. Lincoln committed treason by waging war against the states, if they refused to recognize that they had seceded.