Have to disagree. The South had no Constitutional right to unilaterally leave the Union. And more to the point Lincoln only raised an army AFTER South Carolina attacked Federal troops in a Federal fort. Prior to that he tried to find a peaceful means to solve the issues. Since the South had no inherient right to form a new Country Lincoln never invaded a Sovereign Nation. It is called a "Civil" war for a reason.
Rights not specifically granted/controlled by the Constitution are granted to the states. States vountarily joined the union as an "experiment." No language in law prevented any state from leaving the union as voluntarily as it joined.
IMO, the Southern states had the right to seceed if that was what the voters wanted. I will add, that this argument has been ongoing since the 1860s by the greatest legal minds, with no real conclusion ever reached.
The CSA was a sovereign nation by its own declaration, and only force of arms prevented it from remaining that way. It's only a "civil" war because the North won.
Lincoln hardly was going to find a peaceful solution since his winning the
election is what precipitated secession.
Furthermore the JOB of the President of the United States is to protect and defend the United States. His oath of office required him LEGALLY to solve the issue, the desire of the South to resort to armed conflict gave him no choice but to raise Armies and subdue insurection against legal, Constitutional authority.
It is the job of the President to protect the United States. Since no law precluded states from leaving the US if they so desired, that did not include keeping states as members by force of arms with no legal basis to do so.
Of the States that left the Union only Virginia, North Carolina,South Carolina and Georgia had any technical claim to having freely joined. The other States were purchased by the Federal Government or formed from Federal land given to Settlers. Even Texas was in effect purchased by the US, Texas owed the US a HUGE sum of money and part of the agreement for their joining the Union was that debt was forgiven as well as certain lands ceded or agreed to not contest as US Federal Property.
Texas had every right to seceed, debt or no. Texas was as sovereign nation that joined the US voluntarily, as did all of the Southern states that were part of the original 13 colonies.
You bring up a good point worth considering if and where the US purchased land. Guess it depends on whether or not tha tland was actually purchased, or someone got dispossessed of it.
The only Unconstitutional action taken was the forming of West Virginia as a State. That was clearly Unconstitutional. I believe that eventually the US paid Virginia a compensation for that action.