As soon as Lincoln was elected in 1860, the southern States began to secede from the Union, with South Carolina being the first State to secede, and with Tennessee being the last and the 11th State to secede, although, in fact, the Eastern part of Tennessee remained staunchly pro-union. These eleven States took up arms against their own Federal Government, repudiated Federal debt, conscripted its citizens, and brought on war against their own country, even though Lincoln had made it known in his first Inaugural address that: "The government will not assail you. You can have no conflict without being yourselves the aggressors. You have no oath registered in Heaven to destroy the government, while I shall have the most solemn one to "preserve, protect, and defend it."" The south, though took it upon themselves that if they could not legitimately win by the ballot, and even though Lincoln had assured the south that he would not: "…interfere with the institution of slavery…" none of this prevented the south from taking war into their own hands against their own fellow countrymen.
If would be one thing if the war between the States had been a war of just a few months, and a few thousand deaths, but it is an entirely different thing that the war was instead four long and bloody years, with an incredible amount of destruction of material wealth, along with the deaths of 620,000 men, and countless injuries both physical as well as mental. The South did everything within its power to try to win their "freedom", to create their own country, to make their own Constitution, all without a legitimate and valid reason to do so, while also keeping a significant portion of their fellow human beings in abject poverty and chattel slavery.
Fortunately, for this country, the South was defeated, to which Lincoln was gracious enough to offer to the South, his terms of surrender and the re-admission to the Union, which essentially was permitted when 10% of the population of a given State had pledge both their allegiance to the Union as well as their adherence to the principles of the Emancipation Proclamation. As for the military officers and soldiers of the beaten south, with the exception of certain tribunals set aside for prisoner of war camp abuses, most everyone else was let go on their own recognizance. This meant that no Confederate general, no Confederate politician, such as Jefferson Davis, the President of the Confederacy, suffered the indignity of a trial, of punishment, or execution.
The upshot of confederates not being severely punished was that even though they had been defeated, what we found was that within a very short period of time, it was if the South had never lost the war, as the planter aristocracy asserted their power and influence throughout commerce, law, and politics. Additionally, those that had formerly been slaves with no rights, were now in the South simply slaves in principle, if not in name.
We will never know what would have happened, if instead of the South being treated as errant sons and prodigals, embraced by a loving father; if it had instead been subjected to the full wrath of the American government which was never unleashed, to which if it had the vanquished would have been held accountable for their war crimes and sentenced appropriately for it; as well as undoubtedly we would have seen the commensurate destructionand the evisceration of the Southern aristocracy, which was the real cause of the war, once and for all. This would have left a different South, humbled and occupied, never to rise again on its own undemocratic terms.