The so-called civil war solved nothing. I use the term "so-called" because a civil war, by definition, is a conflict between geographic or political factions of a government fighting for control of that government. The war between the states was fought for the purpose of establishing, or preventing the establishment of, a completely new government.
That the forces of the North prevailed proved only the obvious, a better financed, better armed force, will win over one that is lesser endowed. The question of the South's right to separate itself from the Union, under the constitution as it was then written, is still open for debate.
The United States had no claim over the individual citizens of the several states until after the passage of the fourteenth amendment. Prior to that time a person's citizenship was determined by the state in which he or she resided. The fourteenth amendment created the entity "United States Citizen" and gave the Federal Government the ability to insert itself into matters at the state level under the guise of protecting the rights of US citizens.
While a clever device, the fourteenth amendment still does not address the question of whether states rights are superior or inferior to federal rights.
The framers of the constitution listed what they thought were the ideal limits of Federal power. This list is to be found in the "Enumerated Powers" clause of the Constitution. Several of the original states, leery of the power over their affairs being granted to the federal government, sought assurances that these powers would not be exceeded. Checks on the usurpation of powers was codified in the first ten amendments, chiefly in the tenth.
To more fully understand the intended juxtaposition of power, one must read the word "state" with the meaning that it had during the early years of the nation. In the Declaration of Independence, we find the following: "These United Colonies are, and by right ought to be, Free and Independent States; that they are absolved from all allegiance to the British Crown, and that all political connections between them and the State of Great Britain, is and ought to be totally dissolved." A modern reading gives the alternate meaning of the word "state" as a subdivision of a larger political entity. At the time of the American Revolution it had no such meaning and so the intent of the framers of the Declaration of Independence and of the Constitution is crystal clear on that matter.
It is axiomatic that, in general, people in power will seek to increase the scope of their power. This is no less true of the people who have been elected to national office over the years. Since the very beginning of this great experiment in democracy, those sent to our seat of National Government have treated the Constitution, not as a guide but as a challenge to their skills at finding ways to circumvent the restrictions crafted into it by the Founding Fathers. When such skills failed, the point of a musket took its place.
The Constitution was not written to give power to the Federal government but, rather, to restrict its powers. To say that the Constitution does not give the various States a right to separate themselves from the Union is to look at the matter from the wrong end of the glass. The Constitution does not grant power, it is intended to restrict power.
Our Declaration of Independence is unequivocal on the matter of the right of a people to gain relief from an oppressive government or to separate itself from that government. Nowhere did the Founding Fathers use the term "Perpetual Union" or intimate that they felt they had crafted a Union that would remain forever free from becoming tyrannical. To the contrary, they attempted to word our founding documents in such a way as to prevent the Federal Government from acquiring sufficient power to become overbearing.
Currently there is increasing dissatisfaction with the growth of the Federal Government and we are seeing grass roots movements forming to test again the notion of the right of individual states to be sovereign in matters not covered by the Enumerated Powers Clause. It is interesting to note that our Federal Government, while holding so closely to the notion of our indivisible Union of States, worked so feverishly to bring about the dissolution of the Soviet Union. I suppose their union was held to be "less perpetual."
I am reminded of the ancient Chinese curse: May you live in interesting times.